Variable aperture and actuator assemblies for an imaging system

ABSTRACT

An imaging system which includes a housing for a radiation detector having a window disposed above and in axial alignment with the radiation detector, a variable aperture assembly which includes a base ring having a first opening and mounted on the radiation detector housing such that the first opening is in axial alignment with the window, a plate having a first aperture and adapted to engage the base ring such that the first aperture is disposed over the window, at least one aperture blade each operatively coupled to the base ring, and an aperture drive mechanism having a body and an actuator coupling member extending at an angle from the body. In addition, the imaging system includes an actuator assembly having an actuator and an actuator arm, the actuator arm disposed adjacent to the radiation detector housing in proximity to the actuator coupling member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S. patentapplication Ser. No. 11/761,171 now U.S. Pat. No. 7,724,412, entitled“VARIABLE APERTURE AND ACTUATOR ASSEMBLIES FOR AN IMAGING SYSTEM,” filedon Jun. 11, 2007 and issued May 25, 2010.

FIELD OF THE INVENTION

The present invention relates to imaging systems, more particularly, tovariable aperture assemblies and corresponding actuator assemblies foruse in an imaging system having a radiation detector housing, such as acooled infrared imaging system.

BACKGROUND OF THE INVENTION

Thermal infrared radiation (IR) is emitted from all objects as afunction of their temperature. IR imaging systems are able to detectthermal signatures and identify target objects by analyzing the heat andprofile emitted. The mid-wave and long-wave IR detectors used in IRimaging systems are typically housed in vacuum enclosures, commonlyreferred to as dewars, and cooled to cryogenic temperatures to improvetarget detectability and lower signal to noise ratios.

A conventional IR imaging system 100 employing a typical dewar system102 to cryogenically cool an infrared detector 104 is depicted inFIG. 1. The infrared detector 104 is mounted on a substrate 106 attachedto a cold stem 108 of the dewar system 102. The cold stem 108 houses therefrigeration portion of a stirling cycle refrigerator which cools andmaintains the detector 104 at cryogenic operating temperatures. Thedetector 104 is typically mounted within a coldshield 110 that is housedwithin a vacuum enclosure 112 of the dewar system 102. The vacuumenclosure 112 includes a window 114 attached to the top 116 of thevacuum enclosure 112 that allows the detector 104 to receive radiationsignals external to the vacuum enclosure 112. The optics system of theIR imaging system 100 may be incorporated in the window 114 to thevacuum enclosure 112 or be positioned relative to the window 114 in theexternal housing (not shown in FIG. 1) of the IR imaging system 100.

The coldshield 110 typically includes a fixed aperture 116 thatessentially forms the f-stop for the optics system of the IR while alsoserving as a radiation shield for the detector. Some conventional IRimaging systems are capable of switching between narrow and wide fieldof view window or optics system (e.g., window 114 or the optics systemdisposed in the external housing of the IR imaging system 100) to viewvarious target scenes, which requires two different coldshield aperturesizes to effectively match the optics system. A large family of dewarswith coldshields of different aperture sizes is currently needed toaccommodate the broad range of IR camera system designs. Hence, the needarises for a dewar to have a single coldshield with a variable apertureassembly having two or more apertures that may be switched on command toaccommodate the various optical systems that may be employed in an IRimaging system. Moreover, there is a need for an aperture actuator orcontrol means that does not generate a significant amount of heat withinthe vacuum enclosure when powered on to drive the variable apertureassembly.

U.S. Pat. No. 7,157,706 to Gat et al. discloses variable apertureassemblies (each generally referenced as 122 in FIG. 1) for use in an IRcamera having a dewar system 200 with a detector 104 mounted in acoldshield 110 that is enclosed in a vacuum chamber 112 as shown inFIG. 1. However, each non-magnetic driven variable aperture assembly 122disclosed by Gat requires modifying the vacuum chamber 112 wall toeither (1) add an external aperture control means 120, such as a wormgear system to drive a worm gear attached to the variable apertureassembly 122, or (2) to accommodate a piezoelectric motor aperturecontrol means that directly contacts a friction surface of an outerdrive ring of the variable aperture assembly 122. These conventionalvariable aperture assemblies and corresponding aperture control meansare known to be extremely large in size (requiring significant spacewithin the vacuum chamber or within the external housing of the IRimaging system) and require significant force and travel to control thesize of the variable or swappable aperture to be used.

Accordingly, there is a need for an improved variable aperture assemblyand aperture actuator assembly that overcomes the problems noted aboveand others previously experienced for implementing a variable apertureand actuator within a dewar system of a cooled IR imaging system orcamera.

SUMMARY OF THE INVENTION

In accordance with systems consistent with the present invention, animaging system is provided. The imaging system comprises a housing for aradiation detector (such as a cold shield housing), a variable apertureassembly, and an actuator assembly for the variable aperture. Theradiation detector housing has a window disposed above and in axialalignment with the radiation detector. The variable aperture assemblyincludes a base ring having a first opening and mounted on the radiationdetector housing such that the first opening is in axial alignment withthe window of the radiation detector housing. The variable apertureassembly also includes a plate and at least one aperture blade (e.g., asingle blade, two blades, or four blades) having a first aperture andadapted to engage the base ring such that the first aperture is disposedover the window. Each aperture blade is operatively coupled to the basering so that the respective aperture blade is adapted to move laterallyrelative to the first aperture. The variable aperture further includesan aperture drive mechanism having a body and an actuator couplingmember extending at an angle from the body. The body is operativelycoupled to the base ring and to each aperture blade such that theaperture drive mechanism drives each aperture blade laterally away fromthe first aperture in response to the actuator coupling member beingmoved in a first lateral direction, and laterally over the firstaperture to define a second aperture disposed over the window inresponse to the actuator coupling member being moved in a second lateraldirection. The actuator assembly is disposed adjacent to the radiationdetector housing in proximity to the actuator coupling member. Theactuator assembly has an actuator and an actuator arm. The actuator armhas a first end operatively coupled to the actuator and a second endadapted to engage the actuator coupling member of the aperture drivemechanism so that the actuator controls the lateral movement of theactuator coupling member.

In accordance with articles of manufacture consistent with the presentinvention, a variable aperture assembly for use in an imaging systemhaving a housing for a radiation detector. The housing has a windowdisposed above and in axial alignment with the radiation detector. Thevariable aperture assembly comprises a base ring, a plate disposed overthe base ring, at least one aperture blade, and an aperture drivemechanism. The base ring has a first opening and is adapted to bemounted on the radiation detector housing such that the first opening isin axial alignment with the window. The plate has a first aperture andis adapted to engage the base ring such that the first aperture isdisposed over the window. Each aperture blade is operatively coupled tothe base ring so that each aperture blade is adapted to move laterallyrelative to the first aperture. The aperture drive mechanism has a bodyand an actuator coupling member extending at an angle from the body. Thebody is operatively coupled to the base ring and to each aperture bladesuch that the aperture drive mechanism drives each aperture bladelaterally away from the first aperture in response to the actuatorcoupling member being moved in a first lateral direction, and laterallyover the first aperture to define a second aperture disposed over thewindow in response to the actuator coupling member being moved in asecond lateral direction.

In one implementation of the variable aperture assembly, the at leastone aperture blade includes a first blade having a first end rotatablycoupled at a pivot point to either the base ring or the plate, a secondend adapted to be pivoted relative to the first end, and an innerportion disposed between the first and second ends. The inner portiondefines the second aperture. The base ring or the plate to which thefirst blade is rotatably coupled has an upper surface, a first stop pindisposed on the upper surface away from the pivot point, and a secondstop pin disposed on the upper surface across the first aperture fromthe first stop pin and substantially away from the pivot point. Thefirst stop pin is adapted to engage the second end of the first blade tostop the lateral movement thereof when the first blade is movedlaterally away from the first aperture so that the first aperture isexposed. The second stop pin is adapted to engage the second end of thefirst blade to stop the lateral movement thereof when the first blade ismoved laterally over the first aperture so that the second aperture isdisposed over the window.

In another implementation of the variable aperture assembly, the basering has an outer diameter defining an outer surface and a flangeextending from the outer surface. In this implementation, the body ofthe aperture drive mechanism corresponds to a drive ring adapted torotate about the base ring in sliding contact with the flange of thebase ring. In addition, the base ring may have a plurality of pivot pinscircumferentially spaced on the base ring. The drive ring may have aplurality of drive pins circumferentially spaced on the drive ringrelative to the pivot pins. In this implementation, the at least oneaperture blade corresponds to two or more aperture blades each having afirst end and a second end. The first end of each blade has a pivotopening adapted to receive a respective one of the pivot pins and adrive opening adapted to receive a respective one of the drive pins suchthat the second end of the respective blade is adapted to pivot relativeto the first end when the drive ring is rotated about the base ring.

In another implementation of the variable aperture assembly, the drivering has a plurality of stop pins circumferentially spaced on the drivering such that each drive pin is disposed between a respective two ofthe stop pins. Each aperture blade has a top portion and a lower portionthat collectively form a substantially L-shape having an externalcorner. The lower portion includes the first end and has an outer edge.The top portion includes the second end and has an external edge. Thepivot opening and the drive opening of each aperture blade are disposednear the external corner. Each stop pin is adapted to engage theexternal edge of the top portion of a respective one of the apertureblades to stop the lateral movement thereof when the aperture blade ismoved laterally away from the first aperture so that the first apertureis exposed. Each stop pin may also be adapted to engage the outer edgeof the lower portion of a respective second of the aperture blades tostop the lateral movement thereof when the aperture blade is movedlaterally over the first aperture so that the second aperture isdisposed over the window.

In another implementation of the variable aperture assembly, the platehas a circular outer edge that defines a rim along an outer perimeter ofthe base ring and the body of the aperture drive mechanism correspondsto a drive ring adapted to rotate about the outer edge of the plate insliding contact with the rim of the base ring. The plate has a firstplurality of guide pins circumferentially spaced on the plate. The drivering has a plurality of drive pins circumferentially spaced on the drivering relative to the guide pins. In this implementation, the at leastone aperture blade corresponds to two or more aperture blades. Eachaperture blade has a first guide pin track running in a directionsubstantially parallel to a corresponding radial axis of the window, anda drive pin track running in a direction substantially diagonal to thefirst guide pin track of the aperture blade. Each of the plurality ofdrive pins is operatively coupled to the drive pin track of acorresponding one of the aperture blades such that each drive pintravels along the drive pin track of the corresponding aperture blade inresponse to the drive ring being rotated about the outer edge of theplate. Each of the first plurality of guide pins is operatively coupledto the first guide pin track of a corresponding one of the apertureblades such that each first guide pin travels along the first guide pintrack of the corresponding aperture blade in response to the drive pintraveling along the drive pin track of the corresponding aperture blade.

In accordance with articles of manufacture consistent with the presentinvention, an aperture actuator assembly for use in actuating a variableaperture assembly disposed over a window of radiation detector housingin an imaging device is provided. The variable aperture assemblyincludes an aperture drive mechanism having a body and an actuatorcoupling member extending down at an angle from the body. The actuatorcoupling member is adapted to be moved in a first lateral direction sothat the variable aperture assembly defines a first aperture over thewindow and in a second lateral direction so that the variable apertureassembly defines a second aperture over the window. The apertureactuator assembly comprises an actuator adapted to be disposed adjacentto the radiation detector housing below the actuator coupling member,and an actuator arm disposed between the actuator and the actuatorcoupling member. The actuator arm has a first end operatively coupled tothe actuator and a second end adapted to engage the actuator couplingmember of the aperture drive mechanism so that the actuator controls thelateral movement of the actuator coupling member.

In one implementation of the aperture actuator assembly, the actuator isa piezoelectric motor having an actuator rod operatively coupled to thefirst end of the actuator arm and adapted to be selectively movedbetween a first position to cause the actuator arm to move in the firstlateral direction and a second position to enable the actuator arm tomove in the second lateral direction.

In another implementation of the aperture actuator assembly, theaperture actuator assembly also includes a mounting bracket extendingvertically relative to the radiation detector housing. The actuator armis pivotally coupled to the mounting bracket such that the second end ofthe actuator arm is adapted to rotate in the first lateral direction andthe second lateral direction. The actuator comprises a magnet and avoice coil motor having a wire coil operatively configured to receive adrive current. The wire coil is incorporated in the first end of theactuator arm and the magnet is disposed relative to the wire coil sothat the magnet drives the first end of the actuator arm away from themagnet in a predetermined direction in response to the drive currentflowing through the wire coil. The predetermined direction correspondsto one of the first lateral direction and the second lateral directionbased on a direction of flow of the drive current through the wire coil.

In another implementation of the aperture actuator assembly, theactuator assembly further comprises a mounting bracket extendingvertically relative to the radiation detector housing. The actuator armis pivotally coupled to the mounting bracket such that the second end ofthe actuator arm is adapted to rotate in the first lateral direction andthe second lateral direction. The actuator comprises an electromagneticsolenoid having a drive input and a piston adapted to move along alongitudinal axis of the solenoid between an extended position and acontracted position based on the drive input. The piston has an endoperatively coupled to the first end of the actuator arm so that thepiston drives the second end of the actuator arm in the first lateraldirection when moving towards the extended position and in the secondlateral direction when moving towards the contracted position.

Other systems, methods, features, and advantages of the presentinvention will be or will become apparent to one with skill in the artupon examination of the following figures and detailed description. Itis intended that all such additional systems, methods, features, andadvantages be included within this description, be within the scope ofthe invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate an implementation of the presentinvention and, together with the description, serve to explain theadvantages and principles of the invention. In the drawings:

FIG. 1 is a schematic cross-sectional view of a conventional cooledconventional infrared imaging system having a radiation detector mountedwithin a radiation shield enclosed within a vacuum chamber, where theradiation shield has a variable aperture and a control means for thevariable aperture is mounted external to the vacuum chamber;

FIG. 2 is a schematic cross-sectional view of an exemplary infraredimaging system employing a variable aperture assembly and an apertureactuator assembly consistent with the present invention;

FIG. 3A is a perspective view of one embodiment of a variable apertureassembly and one embodiment of a corresponding aperture actuatorassembly suitable for implementing the present invention in the infraredimaging system in FIG. 2, where the variable aperture assembly includesa plate having a first aperture disposed over a window of an exemplaryradiation detector housing within the infrared imaging system and asingle blade having a second aperture shown in a first positionlaterally away from the first aperture;

FIG. 3B is another perspective view of the variable aperture assemblyand the aperture actuator assembly in FIG. 3A (with a portion of theaperture actuator assembly in partial cut away view), where the singleblade has been moved, via the aperture actuator assembly, in accordancewith the present invention so that the second aperture is in a secondposition over the first aperture and the window of the radiationdetector housing;

FIG. 3C is an exploded view of the variable aperture assembly depictedin FIGS. 3A and 3B;

FIG. 3D is a top view of the variable aperture assembly in which thesecond aperture of the single blade is shown in the first position asdepicted in FIG. 3A;

FIG. 3E is another top view of the variable aperture assembly in whichthe second aperture of the single blade is shown in the second positionas depicted in FIG. 3B;

FIG. 3F is a perspective view of an alternative aperture drive mechanismfor the variable aperture assembly and a corresponding alternativeactuator arm for the aperture actuator assembly in FIGS. 3A and 3B;

FIGS. 4A and 4B are perspective views of a second embodiment of avariable aperture assembly and a second embodiment of a correspondingaperture actuator assembly suitable for implementing the presentinvention in the infrared imaging system in FIG. 2, where the variableaperture assembly includes a fixed plate having a first aperture asshown in FIG. 4A and two aperture blades operatively configured todefine a second aperture over the first aperture when moved via theaperture actuator assembly as shown in FIG. 4B;

FIG. 4C is an exploded view of the variable aperture assembly depictedin FIGS. 4A and 4B;

FIG. 4D is a perspective view of the variable aperture assembly asdepicted in FIG. 4A, where a cover ring of the variable apertureassembly has been removed to provide a more complete view of thearrangement of the two blades when moved via the aperture actuatorassembly to expose the first aperture of the fixed plate;

FIG. 4E is a top view of the variable aperture assembly as depicted inFIG. 4D;

FIG. 4F is a perspective view of the variable aperture assembly asdepicted in FIG. 4B, where the cover ring has been removed to provide amore complete view of the arrangement of the two blades when moved viathe aperture actuator assembly to define the second aperture over thefirst aperture;

FIG. 4G is a top view of the variable aperture assembly as depicted inFIG. 4F;

FIG. 4H is an exploded view of the aperture actuator assembly depictedin FIGS. 4A and B;

FIG. 4I is a perspective view of another implementation (or thirdembodiment) of a aperture actuator assembly suitable for implementingthe present invention in the infrared imaging system in FIG. 2;

FIG. 4J is an exploded view of the aperture actuator assembly depictedin FIG. 4I;

FIGS. 5A and 5B are perspective views of a third embodiment of avariable aperture assembly and a fourth embodiment of a correspondingaperture actuator assembly suitable for implementing the presentinvention in the infrared imaging system in FIG. 2, where the variableaperture assembly includes a fixed plate having a first aperture asshown in FIG. 5A and four aperture blades operatively configured todefine a second aperture over the first aperture when moved via theaperture actuator assembly as shown in FIG. 5B;

FIG. 5C is an exploded view of the variable aperture assembly depictedin FIGS. 5A and 5B;

FIG. 5D is a perspective view of the variable aperture assembly asdepicted in FIG. 5A, where a cover ring of the variable apertureassembly has been removed to provide a more complete view of thearrangement of the four aperture blades when moved via the apertureactuator assembly to expose the first aperture of the fixed plate;

FIG. 5E is a top view of the variable aperture assembly as depicted inFIG. 5D;

FIG. 5F is a perspective view of the variable aperture assembly asdepicted in FIG. 5B, where the cover ring has been removed to provide amore complete view of the arrangement of the four aperture blades whenmoved via the aperture actuator assembly to define the second apertureover the first aperture;

FIG. 5G is a top view of the variable aperture assembly as depicted inFIG. 5F;

FIG. 5H is an enlarged view of one of the aperture blades of thevariable aperture assembly depicted in FIGS. 5A and 5B;

FIG. 5I is an exploded view of the actuator assembly depicted in FIGS.5A and 5B;

FIG. 6 is an exploded view of another implementation (or fourthembodiment) of the variable aperture assembly shown in FIGS. 5A-5G,where the fixed plate has been incorporated into a base ring of thevariable aperture assembly and the base ring has been incorporated intoa window of a radiation detector housing for the infrared imagingsystem;

FIGS. 7A and 7B are perspective views of a fifth embodiment of avariable aperture assembly suitable for implementing the presentinvention, where the variable aperture assembly has four aperture bladesoperatively configured to be selectively adjusted via an apertureactuator assembly consistent with the present invention so as to vary anaperture defined by the aperture blades between a first size shown inFIG. 7A and a second size shown in FIG. 7B;

FIG. 7C is an exploded view of the variable aperture assembly depictedin FIGS. 7A and 7B;

FIG. 7D is a top view of the variable aperture assembly as depicted inFIG. 7A;

FIG. 7E is another top view of the variable aperture assembly depictedin FIGS. 7A & 7B in which the aperture blades have been adjusted via theaperture actuator assembly so that the aperture defined by the apertureblades has a corresponding size that is smaller than the first sizeshown in FIG. 7A and larger than the second size shown in FIG. 7B;

FIG. 7F is a top view of the variable aperture assembly as depicted inFIG. 7B;

FIG. 8A is a top view of another implementation (or sixth embodiment) ofthe variable aperture assembly shown in FIGS. 7A-7G, where each apertureblade of the variable aperture assembly has an S-track or non-lineartrack for controlling the movement of the respective aperture blade andthe size of the aperture collectively defined by each of the blades;

FIG. 8B is a top view of one of the aperture blades of the variableaperture assembly shown in FIG. 8A;

FIGS. 9A and 9B are perspective views of a seventh embodiment of avariable aperture assembly and a fifth embodiment of a correspondingaperture actuator assembly suitable for implementing the presentinvention in the infrared imaging system in FIG. 2, where the variableaperture assembly includes a fixed plate having a first aperture asshown in FIG. 9A and two aperture blades operatively configured todefine a second aperture over the first aperture when moved via theaperture actuator assembly as shown in FIG. 9B; and

FIG. 9C is an exploded view of the variable aperture assembly depictedin FIGS. 9A and 9B.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to an implementation in accordancewith methods, systems, and products consistent with the presentinvention as illustrated in the accompanying drawings.

FIG. 2 depicts a schematic cross-sectional view of an exemplary infraredimaging system 200 employing a variable aperture assembly 202 and anaperture actuator assembly 204 consistent with the present invention.The variable aperture assembly 202, which has a low profile and lowmass, is operatively configured to selectively switch between two ormore apertures of different size so that the selected aperture isaccurately positioned relative to a radiation detector 206 housed withinthe infrared imaging system 200. The aperture actuator assembly 204 alsohas low mass, a compact profile, and a low power actuator that haslimited thermal radiation output suitable for operation in a vacuumenvironment.

As shown in FIG. 2, the infrared imaging system 200 includes a housing208 for the radiation detector 206, which may be one or more pixels in afocal plane array mounted on a substrate 210. The housing 208 has anaperture or window 212 having a fixed size. The window 212 may be anopening in the housing 208 with or without a transparent materialadapted to permit radiation outside the housing 208 within the field ofview of the window 212 to enter the housing 208. The window 212 isdisposed above and in axial alignment with the radiation detector 206.In the implementation shown in FIG. 2, the housing 208 is a cold shieldor radiation shield that is (along with the substrate 210) attached to acold stem 214 of a dewar system 216. In this implementation, theinfrared imaging system 200 also includes a vacuum chamber 218 thatencloses the radiation detector housing 208. The vacuum chamber 218 hasa sealed window 220 over which a variable or fixed lens 222 may bemounted. The cold stem 214 effectively cools and maintains thetemperature of the housing 208 and the radiation detector 206. However,the variable aperture assembly 202 and the aperture actuator assembly204 as described herein may be employed in an uncooled imaging systemwithout departing from the present invention.

In the implementation shown in FIG. 2, the radiation detector 206 andthe housing's window 212 are centrally aligned with each other along alongitudinal or vertical axis 224 of the housing. The variable apertureassembly 202 is mounted over and axially aligned with the housing'swindow 212. The aperture actuator assembly 204 is disposed adjacent toand extending vertically along a side 226 of the radiation detectorhousing 208 and below the variable aperture assembly 202. Although theaperture actuator assembly 204 may employ different actuators asdescribed herein, the aperture actuator assembly 204 has a compactprofile, with a volume (e.g., width, height, and depth shown as w, h andd in FIGS. 3A-B, w′, h′ and d′ in FIGS. 4A-4B, and w″, h″, and d″ inFIGS. 5A-5B) within a range from 13 cubic mm to 3750 cubic mm based on awidth (i.e., w, w′ or w″) ranging from 1.5 mm to 25 mm, a height (i.e.,h, h′ or h″) ranging from 1.5 mm to 25 mm, and a depth of approximately6 mm. The compact profile of the aperture actuator assembly 204 enablesthe aperture actuator assembly 204 to engage and actuate the variableaperture assembly 202 while disposed and operating in the vacuum chamber218 of the imaging system 200.

Various embodiments of the variable aperture assembly 202 consistentwith the present invention are described herein. Each variable apertureassembly 202 (300 in FIGS. 3A-3F, 400 in FIGS. 4A-4G, 500 in FIGS.5A-5H, 600 in FIG. 6, 700 in FIGS. 7A-7F, 800 in FIGS. 8A-8F, and 900 inFIGS. 9A-9C) may include a base ring 228 (306 in FIG. 3C, 404 in FIG.4C, 504 in FIG. 5C, 604 in FIG. 6, 704 in FIG. 7C, or 904 in FIG. 9C)having a first opening 230 (308 in FIG. 3C, 406 in FIG. 4C, 506 in FIG.5C, 706 in FIG. 7C or 906 in FIG. 9C) and mounted on the radiationdetector housing 208 such that the first opening 230 is in axialalignment with the window 212 of the housing 208. Each variable apertureassembly may include a plate 232 (310 in FIG. 3C, 426 in FIG. 4C, 526 inFIG. 5C, 726 in FIG. 7C or 926 in FIG. 9C) having a first aperture 234(312 in FIG. 3C, 428 in FIG. 4C, 528 in FIG. 5C, 728 in FIG. 7C or 928in FIG. 9C) of a fixed size, where the plate 232 is mounted to and/oradapted to engage the base ring 228 such that the first aperture 234 isdisposed over and in axial alignment with the housing's window 212. Asdiscussed in reference to FIG. 6, the plate 232 may be incorporated intothe base ring 228 and the base ring 228 affixed or incorporated into thetop 236 of the radiation detector housing 208 so that the housing window212 corresponds to the first aperture 234.

Each variable aperture assembly also has one or more aperture blades 238(332 in FIG. 3C, 438 and 440 in FIG. 4C, 538 a-538 b in FIG. 5C, 738a-738 b in FIG. 7C, 838 a-838 b in FIG. 8C or 938 a-938 b in FIG. 9C)and an aperture drive mechanism 240 (334 in FIG. 3C, 410 in FIG. 4C, 510in FIG. 5C, 710 in FIG. 7C or 910 in FIG. 9C). As explained in furtherdetail below, each aperture blade 238 is operatively coupled to the basering 228 or plate 232 so that the respective aperture blade 238 isadapted to move laterally relative to the first aperture 234. Theaperture drive mechanism 240 has a body 242 and an actuator couplingmember 244 extending at an angle from the body 242, allowing theactuator assembly 204 to be disposed next to (or abut) the radiationdetector housing 208 and within the vacuum chamber 218.

As described in further detail below, the body 242 of the aperture drivemechanism 240 is operatively coupled to the base ring 228 (or the plate232 having the first aperture 234) and to each aperture blade 238 suchthat the aperture drive mechanism 240 drives each aperture blade 238laterally away from the first aperture 234 in response to the actuatorcoupling member 244 being moved in a first lateral direction (e.g.,direction reflected by arrow 370 a in FIGS. 3A, 4A and 5A, arrow 757 ain FIG. 7A, or arrow 957 a in FIG. 9A), and laterally over the firstaperture 234 to define a second aperture 246 disposed over the radiationdetector housing window 212 in response to the actuator coupling member244 being moved in a second lateral direction (e.g., direction reflectedby arrow 370 b in FIGS. 3B, 4B and 5B, arrow 757 b in FIG. 7B, or arrow957 b in FIG. 9B).

Various embodiments of the aperture actuator assembly 204 consistentwith the present invention are also described herein. Each actuatorassembly 204 (302 in FIGS. 3A-3B, 402 in FIGS. 4A-4B and 4H, 402 a inFIGS. 4I-4J, 502 in FIGS. 5A-5B and 5I, and 902 in FIGS. 9A-9B) may beemployed in accordance with the present invention to drive any one ofthe variable aperture assemblies 202, 300, 400, 500, 600, 700, 800, and900. As discussed in further detail below, each actuator assembly has anactuator 248 (380 in FIGS. 3A-3B, 3F and 7A-7B, 402 in FIGS. 4A-4B and4H, 402 a in FIGS. 4I-4J, 502 in FIGS. 5A-5B and 5I, and 902 in FIGS.9A-9B) and an actuator arm 250 (354 in FIGS. 3A-3B and 7A-7B, 364 inFIG. 3F, 416 in FIGS. 4A-4B and 4H-4J, 516 in FIGS. 5A-5B and 5I, and966 in FIGS. 9A-9B). The actuator arm 250 has a first end 252operatively coupled to the actuator 248 and a second end 254 adapted toengage the actuator coupling member 244 of the aperture drive mechanism240 so that the actuator 248 controls the lateral movement of theactuator coupling member 244. The actuator 248 of each actuator assembly204 includes one or more interconnects 254 to route power inputs signals(e.g., a drive input signal or current and a return output signal orcurrent for the actuator 248) and other signals between the respectiveactuator 248 and a drive motor or a backend processor (not shown infigures) which may be disposed external to the vacuum chamber 218 of theimaging system 200.

FIGS. 3A-3E depict one embodiment of a variable aperture assembly 300and FIGS. 3A-3B depict one embodiment of a corresponding apertureactuator assembly 302 suitable for implementing the present invention inthe infrared imaging system 200. Components of the imaging system 200,such as the vacuum chamber 218, are not shown in FIGS. 3A-3E to avoidobscuring inventive aspects of the variable aperture assembly 300 andthe aperture actuator assembly 302.

The radiation detector housing 304 shown in FIGS. 3A-3C has a hour glassshape but is otherwise consistent with the housing 208 shown in FIG. 2.The radiation detector housing 304 has an aperture or window 206disposed above and in axial alignment with the radiation detector 206(not shown in FIGS. 3A-3C). The variable aperture assembly 300 includesa base ring 306 having a first opening 308 and mounted on the radiationdetector housing 304 such that the first opening 308 is in axialalignment with the window 206. The base ring 306 may be mounted to theradiation detector housing 304 via epoxy, soldering, or other fasteningtechnique. A plate 310 having a first aperture 312 is engaged orattached to the base ring 306 such that the first aperture 312 isdisposed over the window 206. The base ring 306 and the plate 310 mayeach be comprised of a conductive metal or alloy that allows heatproduced by the variable aperture assembly or received from radiationincident on the variable aperture assembly to be dissipated via thehousing 304, which may function as a cold shield as previouslydiscussed. In the implementation shown in FIGS. 3A-3E, the base ring 306has an upper surface 314 and a plurality of pins 316, 318, 320 and 322extending from the upper surface 314. The plate 310 also has an uppersurface 323 defining a number of openings 324, 326, 328 and 330 eachoperatively configured to receive and retain a corresponding one of thepins 316, 318, 320 and 322 so that the first aperture 312 is disposedover and accurately aligned with the window 206. Alternatively, the basering 306 may be formed to incorporate the plate so that the base ring306 has the first aperture 312.

The variable aperture assembly 300 also includes a single or firstaperture blade 332 that is operatively coupled to the base ring 306 orthe plate 310 so that the aperture blade 332 is adapted to movelaterally relative to the first aperture 312. In the implementationshown in FIGS. 3A-3E, the aperture blade 332 has a first end 334, asecond end 336, and an inner portion 338 disposed between the first andsecond ends where the inner portion 338 defines the second aperture 340.The aperture blade 332 is rotatably coupled at a pivot point (e.g., pin320, which functions as a pivot pin) to either the base ring 306, theplate 310, or both. The second end 336 of the aperture blade 332 isadapted to be pivoted relative to the first end 334. In theimplementation shown in FIGS. 3A-3E, the aperture blade 332 defines apivot opening 341 that is adapted to receive and retain the pivot pin320. In an alternate implementation, the pivot opening 341 may bedefined by the base ring 306 or the plate 310 having the first aperture312 while the pivot pin 320 is on a lower surface of the aperture blade332. In either implementation, the pivot opening 341 and the pivot pin320 engaged in the pivot opening 341 collectively define the pivot pointfor the aperture blade 332 relative to the first aperture 312.

As shown in FIGS. 3A-3E, the first end 334 and the second end 336 of theaperture blade 332 may be extensions or projections of the inner portion338. Alternatively, the first end 334 and the second end 336 may beopposing external sections of the inner portion 338, which may have asubstantially circular, elliptical, square or other shape. The innerportion 338, however, has a size that is greater than the size of thefirst aperture 312 to enable the inner portion 338 to partially overlapthe plate 310 when the aperture blade 332 is moved laterally over thefirst aperture 312 such that the second aperture 340 is axially alignedwith the first aperture 312 and the underlying window 206 of theradiation detector housing 304 as shown in FIGS. 3B and 3E.

In one implementation, a first stop pin (e.g., pin 318) is disposed onthe upper surface 314 or 323 of either the base ring 306 or the plate310 away from the pivot point (e.g., pin 320). A second stop pin (e.g.,pin 316) is disposed on the upper surface 314 or 323 across the firstaperture 312 from the first stop pin 318 and substantially away from thepivot point or pin 320. As shown in FIGS. 3A-3E, the pivot pin 320, thefirst stop pin 318 and the second stop pin 316 are arranged in atriangular pattern about the first aperture 312. The first stop pin 318is positioned relative to the pivot pin 320 so that the first stop pin318 is adapted to engage the second end 336 of the aperture blade 332 tostop the lateral movement thereof when the aperture blade 332 is movedlaterally away from the first aperture 312 and the first aperture 312 isexposed. The second stop pin 316 is positioned relative to the pivot pin320 so that the second stop pin 316 is adapted to engage the second end336 of the aperture blade 332 to stop the lateral movement thereof whenthe aperture blade 332 is moved laterally over the first aperture 312 sothat the second aperture 340 is disposed over and in axial alignmentwith the window 206 of the radiation detector housing 304.

In one implementation, the plate 310 includes a lobed section 342disposed relative to the first stop pin 318 and the pivot pin 320 sothat the inner portion 338 of the aperture blade 332 rests on the lobedsection 342 when the second end 336 of the aperture blade 332 engagesthe first stop pin 318 and the first aperture 312 is exposed. To furtherdecrease the weight and mass of the variable aperture assembly 300, acentral portion 344 of the lobed section 342 may be removed. Inaddition, the lobed section 342 allows sufficient thermal conductivitywith the plate 312, base ring 306, and the radiation detector housing304 so as to maintain the aperture blade 332 at a uniform operationaltemperature that otherwise might be elevated due to the incident thermalradiation thereon when the inner portion 338 of the blade 332 is or isnot resting on the lobed section 342.

As shown in FIGS. 3A-3E, the variable aperture assembly 300 alsoincludes an aperture drive mechanism 344 having a body 346 and anactuator coupling member 348 extending at an angle 350 from the body 346such that the actuator assembly 302 (or actuator assembly 402, 402 a,502 or 902 described herein) may engage the actuator coupling member 348and drive the aperture drive mechanism 344 while being disposed next tothe radiation detector housing 304 and within the vacuum chamber 218 ofthe imaging system 200. In the implementation shown in FIGS. 3A and 3B,the actuator coupling member 348 includes a rod 352 extending down fromand perpendicular to the body 346 of the aperture drive mechanism 344.In this implementation, the actuator assembly 302 includes an actuatorarm 354 that has a recess 356 (e.g., defined by pins 358 a and 358 b) onone end 360 of the actuator arm 354. The recess 356 is adapted to engageand laterally retain the rod 352 so that the actuator arm 354 controlsthe lateral movement of the aperture drive mechanism 344. The actuatorarm 354 may be comprised of titanium, plastic, or other poor thermalconducting material that is also low in friction to improve reliability.

FIG. 3F is a perspective view of an alternative aperture drive mechanism362 for the variable aperture assembly 300 and a correspondingalternative actuator arm 364 for the aperture actuator assembly 302. Theactuator arm 364 is consistent with the actuator arm 354 except that theactuator arm 364 includes a rod 365 instead of a recess 356. The rod 365extends from the end 366 of the actuator arm 364 toward the aperturedrive mechanism 362. The aperture drive mechanism 362 is consistent withthe aperture drive mechanism 344 except that the actuator couplingmember 367 of the aperture drive mechanism 362 has a flange 368 insteadof a rod 352 extending down from and perpendicular to the body 346 ofthe aperture drive mechanism 362. The flange 368 has an opening 369adapted to receive and laterally retain the rod 365 on the actuator arm364 of the actuator assembly 302 shown in FIG. 3F so that the actuatorarm 364 controls the lateral movement of the aperture drive mechanism344.

As shown in FIGS. 3A-3F, the body 346 of the aperture drive mechanism344 and 362 is operatively coupled to the base ring 306 and to eachaperture blade 332 such that the aperture drive mechanism 344 or 362drives each aperture blade 332 laterally away from the first aperture312 in response to the actuator coupling member 348 or 367 being movedin a first lateral direction (e.g., direction reflected by arrow 370 ain FIG. 3A), and laterally over the first aperture 312 to define or movethe second aperture 340 over the window 206 in response to the actuatorcoupling member 348 or 367 being moved in a second lateral direction(e.g., direction reflected by arrow 370 b in FIG. 3B).

In the implementation shown in FIGS. 3A-3F, the body 346 of the aperturedrive mechanism 344 and 362 corresponds to a drive arm that includes afirst end 372 a and a second end 372 b. The first end 372 a is pivotallycoupled near the pivot point (e.g., pin 320 and pivot opening 341) tothe aperture blade 332. The first end 372 a of the body 346 or drive armhas a drive pin 373 that is received and retained by a drive opening 374(shown best in FIG. 3C) defined near the pivot opening 341 by theaperture blade 332. In an alternate implementation, the first end 372 aof the body 346 or drive arm may define the drive opening 374 and thedrive pin 373 may be disposed on the aperture blade 332 near the pivotpoint corresponding to the pivot opening 341.

The second end 372 b of the body 346 or drive arm has a track 376adapted to receive and control the lateral movement of a third stop pin(e.g., pin 322) disposed on the upper surface 316 or 323 of the basering 306 or the plate 310 when engaged to the base ring 306. The track376 of the drive arm defines a lateral travel range for the aperturedrive mechanism 344. The track 376 has a first terminal 377 a adapted toengage the third stop pin 322 when the actuator coupling member 348 ismoved in the first lateral direction 370 a so that the aperture blade332 is rotated away from the first aperture 312 to a first positionwhere the second end 336 of the aperture blade 332 is engaged by thefirst stop pin 318 as shown in FIGS. 3A and 3D. The track 376 also has asecond terminal 377 b adapted to engage the third stop pin 322 when theactuator coupling member 348 is moved in the second lateral direction370 b so that the aperture blade 332 is rotated over the first aperture312 to a second position where the second end 336 of the aperture blade332 is engaged by the second stop pin 316 as shown in FIGS. 3B, 3E and3F.

As shown in FIGS. 3A, 3B and 3F, the actuator arm 354 and 364 each havea first end 378 operatively coupled to an actuator 380 of the actuatorassembly 302 and a second end 360, which (as previously discussed) isadapted to engage the actuator coupling member 348 or 367 of theaperture drive mechanism 346 or 362 so that the actuator 380 controlsthe lateral movement of the actuator coupling member 348 or 367. In theimplementation shown in FIGS. 3A and 3B, the actuator 380 includes apiezoelectric motor 381 having an actuator rod 382. The actuator rod 382is operatively coupled to the first end 378 of the actuator arm 354 or364 and is adapted to be selectively moved between a first position(such as shown in FIG. 3A) to cause the actuator arm 354 or 364 to movein the first lateral direction 370 a and a second position (such asshown in FIG. 3B) to enable the actuator arm 354 or 364 to move in thesecond lateral direction 370 b.

The actuator assembly 302 may also include a mounting bracket 383extending vertically relative to the radiation detector housing 304. Theactuator arm 354 or 364 may be operatively coupled to the mountingbracket 383 such that the second end 360 of the actuator arm 354 or 364is adapted to move in the first lateral direction 370 a and the secondlateral direction 370 b. In one implementation, the actuator assembly302 includes an L-shaped linkage member 384 operatively coupled betweenthe first end 378 of the actuator arm 354 or 364 and the actuator rod382 of the piezoelectric motor 381. The linkage member 384 has a firstend 385, a second end 386, and a corner 387 that is pivotally attachedto the mounting bracket 383 via a pin 398, a torsion spring or otherpivoting means. The first end 385 is pivotally coupled (e.g., via a pin388) to the first end 378 of the actuator arm 354 or 364. The linkagemember 384 also has a flange 389 disposed at or near the second end 386of the linkage member 384. The actuator rod 382 of the piezoelectricmotor 381 is disposed relative to the flange 389 so that the actuatorrod 382 is adapted to engage the flange 389 when moving from the firstposition to the second position such that the first end 385 of thelinkage member 384 pivots about the corner 387 and drives the second end360 or 366 of the actuator arm 354 or 364 in a corresponding one of thefirst lateral direction 370 a or the second lateral direction 370 b. Forexample, in the implementation shown in FIG. 3B, the actuator rod 382 ofthe piezoelectric motor 381 is adapted to engage and drive the flange389 downward when moving from the first position to the second positioncausing the first end 385 of the linkage member 384 to pivot about thecorner 387 and drive the second end 360 or 366 of the actuator arm 354or 364 in the second lateral direction 370 b.

As shown in FIGS. 3A and 3B, the actuator assembly 302 may also includea bias member 390 (such as a spring, torsion bar, elastic band or otherbias member) operatively coupled between the vertical mounting bracket383 and a point (e.g., a pin 391 affixed to the linkage member 384) nearthe second end 386 of the linkage member 384 to bias the flange 389vertically when the actuator rod 382 of the piezoelectric motor 381 ismoved towards the first position. Accordingly, when the actuator rod 382of the piezoelectric motor 381 is moved towards the first position andaway from the flange 389, the bias member 390 biases the first end 385of the linkage member 384 to pivot about the corner 387 of the linkagemember 384 so that the second end 360 of the actuator arm is driven inanother of the first lateral direction 370 a or the second lateraldirection 370 b. For example, in the implementation shown in FIG. 3A,when moving from the second position to the first position, the actuatorrod 382 of the piezoelectric motor 381 moves away from the flange 389and the bias member 390 biases the first end 385 of the linkage memberso that the first end 385 of the linkage member 384 pivots about thecorner 387 and drives the second end 360 of the actuator arm 354 or 364in the first lateral direction 370 a.

FIGS. 4A-4G depict a second embodiment of a variable aperture assembly400 and FIGS. 4A, 4B and 4H depict a second embodiment of acorresponding aperture actuator assembly 402 suitable for implementingthe present invention in the infrared imaging system 200 having aradiation detector housing 304. Again, components of the imaging system200, such as the vacuum chamber 218, are not shown in FIGS. 4A-4H toavoid obscuring inventive aspects of the variable aperture assembly 400and the aperture actuator assembly 402.

The variable aperture assembly 400 includes a base ring 404, a plate 426having a fixed aperture 428, two aperture blades 438 and 440, and anaperture drive mechanism 410. The base ring 404 has a first opening 406and is mounted on the radiation detector housing 304 such that the firstopening 406 is in axial alignment with the window 206 of the housing304. The base ring 404 may be mounted to the radiation detector housing304 via epoxy, soldering, or other fastening technique. The base ring404 and the plate 426 may each be comprised of a conductive metal oralloy that allows heat produced by the variable aperture assembly orreceived from radiation incident on the variable aperture assembly to bedissipated via the housing 304. The base ring 404 has an outer diameter407 that defines an outer surface 408. The base ring 404 also has aflange 409 extending from the outer surface 408. In one implementation,the flange 409 is one of a plurality of flanges 409 circumferentiallyspaced about the base ring 404.

The aperture drive mechanism 410 has a body 411 and an actuator couplingmember 412 extending at an angle 413 from the body 411 such that theactuator assembly 402 (or actuator assembly 302, 402 a, or 502 describedherein) may engage the actuator coupling member 412 and drive theaperture drive mechanism 410 while being disposed next to the radiationdetector housing 304 and within the vacuum chamber 218 of the imagingsystem 200. In the implementation shown in FIGS. 4A-4G, the actuatorcoupling member 412 includes a rod 414 extending down from andperpendicular to the body 411 of the aperture drive mechanism 410. Inthis implementation, the actuator assembly 402 includes an actuator arm416 having a recess 418 (e.g., defined by pins 419 and 420 in FIG. 4H)on one end 422 (i.e., the second end) of the actuator arm 416. Therecess 418 is adapted to engage and laterally retain the rod 414 of theactuator coupling member 412 so that the actuator arm 416 controls thelateral movement of the aperture drive mechanism 410. As furtherdiscussed below, the actuator assembly 402 includes a rotary actuator423 operatively coupled to another end 424 (i.e., the first end) of theactuator arm 416 and adapted to control the rotational movement of theactuator arm 416. The actuator arm 416 may be comprised of titanium,plastic, or other poor thermal conducting material that is also low infriction to improve reliability.

In an alternative implementation, instead of a recess 418, the actuatorarm 416 may have a rod 365 on the one end 422 (consistent with the rod365 on the actuator arm 354 in FIG. 3F), where the rod 365 extendstoward the aperture drive mechanism 410. In this implementation, theactuator coupling member 412 of the aperture drive mechanism 410 mayhave a flange 368 having an opening 369 instead of a rod 414 consistentwith the aperture drive mechanism 362 in FIG. 3F. As previouslydiscussed, the flange opening 369 is adapted to receive and laterallyretain the rod 365 on the actuator arm of the actuator assembly so thatthe actuator arm controls the lateral movement of the aperture drivemechanism 410.

In the implementation of the variable aperture assembly 400 shown inFIGS. 4A-4G, the body 411 of the aperture drive mechanism 410corresponds to a drive ring adapted to rotate about the base ring 404 insliding contact with the one or more flanges 409 extending from theouter surface 408 of the base ring 404. In this implementation, thedrive ring 411 has an inner diameter 425 that is equal to or larger thanthe outer diameter 407 of the base ring 404.

The plate 426 having the first aperture 428 is engaged or attached tothe base ring 404 such that the first aperture 428 is disposed over thewindow 206 of the housing 304. In the implementation shown in FIGS.4A-4G, the base ring 404 has an upper surface 430 and a plurality ofpins 432 and 433 extending from the upper surface 430. The plate 426also has an upper surface 434 defining a number of openings 436 and 437each operatively configured to receive and retain a corresponding one ofthe pins 432 and 433 so that the first aperture 428 is disposed over andaccurately aligned with the window 206 of the housing 304.Alternatively, the base ring 404 may be formed to incorporate the plate426 so that the base ring 404 has the first aperture 428.

Each of the two aperture blades 438 and 440 are operatively coupled tothe base ring 404 or the plate 426 so that each aperture blade 438 and440 is adapted to move laterally relative to the first aperture 428. Inthe implementation shown in FIGS. 4A-4G, each aperture blade 438 and 440has a first end 442 or 443, a second end 444 or 445, and a front edge446 and 447. The first end 442 or 443 of each blade 438 and 440 has apivot opening 450 adapted to receive a respective one of a plurality ofpivot pins (e.g., pins 432 and 433) circumferentially spaced on theupper surface 430 of the base ring 404. The first end 442 or 443 of eachblade 438 and 440 also has a drive opening 452 adapted to receive arespective one of a plurality of drive pins 454 and 456circumferentially spaced on the drive ring 411 relative to the pivotpins 432 and 433 on the base ring 404 such that the second end 444 or445 of the respective blade 438 or 440 is adapted to pivot relative tothe first end 442 or 443 when the drive ring 411 is rotated about thebase ring 404. As further described herein, the front edge 446 or 447 ofeach aperture blade 438 and 440 collectively define a second aperture448 that is disposed over the radiation detector housing's window 206 inresponse to the actuator coupling member 412 (or rod 414) being moved ina the second lateral direction 370 b so that the drive ring 411 isrotated in the same direction about the base ring 404 as shown in FIGS.4B, 4F and 4G.

In an alternative implementation, each pivot opening 450 may be definedby the base ring 404 or the plate 426 having the first aperture 428while a respective pivot pin 432 or 433 is disposed on a lower surfaceof the first end 442 or 444 of a respective aperture blade 438 or 440.In either implementation, each pivot opening 450 and the pivot pin 432or 433 engaged in the pivot opening 450 collectively define the pivotpoint for the respective aperture blade 438 or 440.

The drive ring 411 may also have a plurality of stop pins 458 and 459circumferentially spaced on the drive ring 411 such that each drive pin454 and 456 is disposed between a respective two of the stop pins 458and 459. Each stop pin 458 and 459 is adapted to engage the second end444 or 445 of a respective one of the aperture blades 438 or 440 to stopthe lateral movement thereof when the aperture blade 438 or 440 is movedlaterally away from the first aperture 428 so that the first aperture428 is exposed as shown in FIGS. 4A, 4D and 4E.

Each pivot pin 432 and 433 (when received in the pivot opening 450 ofthe respective aperture blade 438 or 440) may also be adapted to engagethe second end 444 or 445 of a respective second or adjacent one of theaperture blades 440 or 438 to stop the lateral movement thereof when theaperture blade 440 or 438 is moved laterally over the first aperture 428so that the second aperture 448 is collectively defined by the frontedges 446 and 447 of the blades and disposed over the window 206 of theradiation detector housing 304 as shown in FIGS. 4B, 4F and 4G.

As described herein, the drive ring 411 (i.e., the body of the aperturedrive mechanism 410) is operatively coupled to the base ring 404 viasliding engagement with the flange 409 extending from the outer surface408 of the base ring 404. The drive ring 411 is also operatively coupledto each aperture blade 438 and 440 via a respective drive pin 454 or456. The aperture drive mechanism 410 is adapted to drive each apertureblade 438 and 440 about a respective pivot pin 432 and 433 so that eachaperture blade 438 and 440 moves laterally away from the first aperture428 in response to the actuator coupling member 412 (which extends fromthe drive ring 411) being moved in the first lateral direction (e.g.,direction reflected by arrow 370 a in FIG. 4A). In addition, the drivemechanism 410 is adapted to drive each aperture blade 438 and 440 in areverse direction about a respective pivot pin 432 and 433 so that eachaperture blade 438 and 440 moves laterally over the first aperture 428to define the second aperture 448 over the window 206 in response to theactuator coupling member 412 being moved in the second lateral direction(e.g., direction reflected by arrow 370 b in FIG. 4B).

As shown in FIGS. 4A, 4B and 4C, the variable aperture assembly 400 mayalso include a cover ring 460 having an inner aperture 462 that has asize equal to or greater than the size of the first aperture 428. Thecover ring 460 is disposed over and vertically retains or captivates theaperture blades 438 and 440 to the base ring 404 and/or the drive ring410. In one implementation, the cover ring 460 is attached to the pivotpins 432 and 433 so that the cover ring 460 is suspended above theaperture blades 438 and 440 so that each aperture blade 438 and 440 isadapted to freely rotate about a respective pivot pin 432 or 433 betweena respective stop pin 458 or 459 and a respective drive pin 454 and 456.

Turning again to the actuator assembly 402 shown in FIGS. 4A, 4B and 4H,the actuator assembly 402 includes a mounting bracket 464 extendingvertically relative to the radiation detector housing 304. The actuatorarm 416 is pivotally coupled to the mounting bracket (e.g., via a pin465) such that the second end 422 of the actuator arm is adapted torotate in the first lateral direction 370 a and the second lateraldirection 370 b.

In the implementation shown in FIGS. 4A, 4B and 4H, the rotary actuator423 is a voice coil actuator that includes a voice coil motor 466. Thevoice coil motor 466 comprises a wire coil 467 and one or more magnets468 a and 468 b, each of which may be a permanent or non-permanentmagnet. The wire coil 467 is incorporated in the actuator arm 416 nearthe first end 424. The wire coil 467 is operatively configured toreceive a drive current via a drive current motor (not shown in thefigures). Each magnet 468 a-468 b is disposed relative to the wire coil467 so that the respective magnet 468 a-468 b drives the first end 424of the actuator arm 416 away from the magnet 468 a or 468 b in apredetermined direction in response to the drive current flowing throughthe wire coil 467. The predetermined direction of the first end 424 ofthe actuator arm corresponds to either the first lateral direction 370 aor the second lateral direction 370 b (opposite to the lateral directionof movement of the second end 422 as shown in the figures) based on thedirection of flow of the drive current through the wire coil 467.

In the implementation shown in FIGS. 4A, 4B, and 4H, the wire coil 467is disposed between a pair of magnets 468 a and 468 b so that, when adrive current is flowing through the wire coil 467, the magnetic fieldproduced by each of the magnets 468 a and 468 b drives or forces thefirst end 424 of the actuator arm 416 (which has the wire coil 467)about the pivot pin 465 in the predetermined direction corresponding tothe direction of flow of the drive current. The second end 422 of theactuator arm 216 then drives the actuator coupling member 412 of theaperture drive mechanism 410 in a corresponding lateral direction (e.g.,opposite to the lateral movement of the first end 424). The amount oflateral travel of each end 422 and 424 of the actuator arm 416 iscontrolled by the amplitude of the drive current received by and flowingthrough the wire coil 467.

A first of the pair of magnets 468 a is affixed to the vertical mountingplate 464. A second of the pair of magnets 468 b may be affixed to across bracket 470 that is attached to either or both sides 472 a and 472b of the mounting bracket 464 such that the first end 424 of theactuator arm 416 may rotate freely about the pivot pin 465 and betweenthe pair of magnets 468 a and 468 b without contacting or engaging thecross bracket 470. Each magnet 468 a and 468 b may have an arcuate shapeand a respective length that enables the wire coil 467 to remain atleast partially between the pair of magnets 468 a and 468 b as the firstend 424 of the actuator arm 416 is rotated about the pivot pin 465.

In one implementation, the first end 424 of the actuator arm 416 has anarcuate outer surface 474 having a plurality of detents 475 a-475 ecorresponding to a plurality of predetermined positions for the actuatorarm 416. The actuator assembly 402 further comprises a spring pin 476having a first end 477 attached to one of the brackets 464 or 470, or toone of the magnets 468 a or 468 b. The spring pin 476 has a second end478 disposed relative to the first end 424 of the actuator arm 416 suchthat the spring pin 476 is adapted to removably engage one (e.g., 475 b)of the plurality of detents 475 a-475 e to retain the actuator arm 416in a corresponding one of the predetermined positions when the drivecurrent is not flowing through the wire coil 467. When the drive currentis flowing through the wire coil 467, the magnetic field produced byeach magnet 468 a and 468 b (collectively or alone) may be sufficient tocause the actuator arm 416 to move and disengage the spring pin 476 fromthe one detent (e.g., 475 b).

FIGS. 4I and 4J depict another implementation of an aperture actuatorassembly 402 a suitable for implementing the present invention in theinfrared imaging system 200. The aperture actuator assembly 402 a hascomponents consistent with the actuator assembly 402 except that, inlieu of a spring pin 476 and detents 475 a-475 e on the second end 424of the actuator arm 416, one of the actuator arm 416 and the mountingbracket 464 has a metal portion 482, and the other of the actuator arm416 and the mounting bracket 464 has a restraining magnet 483 disposedrelative to and having an attraction for the metal portion 482. In thisimplementation, the restraining magnet 483 has sufficient attraction tothe metal portion 482 so that the restraining magnet 483 is adapted toretain the actuator arm 416 in its current rotated position when thedrive current is not flowing through the wire coil. When the drivecurrent is flowing through the wire coil 467, the magnetic fieldproduced by each magnet 468 a and 468 b (collectively or alone) may besufficient to cause the actuator arm 416 to move and disengage theattraction of the restraining magnet 464 to the metal portion 483.

Alternatively, as shown in FIGS. 4I and 4J, in lieu of or in addition tothe detents 475 a-475 e, the actuator arm 416 may have a plurality ofdetent magnets 484 a-484 e corresponding to a plurality of predeterminedpositions for the actuator arm 416. Each detent magnet 484 a-484 e has afirst polarity. The restraining magnet 483 has a second polarity. Therestraining magnet 483 is disposed on the mounting bracket 464 relativeto the plurality of detent magnets 484 a-484 e such that the restrainingmagnet 483 is attracted to a closest one of the detent magnets 484 a-484e to retain the actuator arm 416 in a corresponding one of thepredetermined positions when the drive current is not flowing throughthe wire coil 467. When the drive current is flowing through the wirecoil 467, the magnetic field produced by each magnet 468 a and 468 b(collectively or alone) may be sufficient to cause the actuator arm 416to move and disengage the attraction of the restraining magnet 464 tothe detent magnets 484 a-484 e.

It is contemplated that the restraining magnet 483 may be disposed onthe actuator arm 416 and the detent magnets 484 a-484 e may be disposedon the mounting bracket 464 relative to the restraining magnet 483 suchthat the restraining magnet 483 is attracted to a closest one of thedetent magnets 484 a-484 e to retain the actuator arm 416 in acorresponding one of the predetermined positions when the drive currentis not flowing through the wire coil.

FIGS. 5A-5H depict a third embodiment of a variable aperture assembly500 and FIGS. 5A, 5B and 5I depict a fourth embodiment of acorresponding aperture actuator assembly 502 suitable for implementingthe present invention in the infrared imaging system 200 having aradiation detector housing 304. The variable aperture assembly 500includes a base ring 504, a plate 526 having a fixed aperture 528, fouraperture blades 538 a-538 d and an aperture drive mechanism 510. Thebase ring 504 has a first opening 506 and mounted on the radiationdetector housing 304 such that the first opening 506 is in axialalignment with the window 206 of the housing 304. The base ring 504 maybe mounted to the radiation detector housing 304 via epoxy, soldering,or other fastening technique. As previously discussed, the base ring 504and the plate 526 may each be comprised of a conductive metal or alloythat allows heat produced by the variable aperture assembly 500 orreceived from radiation incident on the variable aperture assembly 500to be dissipated via the housing 304. The base ring 504 has an outerdiameter 507 that defines an outer surface 508 and a flange 509extending from the outer surface 508. The flange 509 may be one of aplurality of flanges 509 circumferentially spaced about the base ring504.

The aperture drive mechanism 510 has a body 511 and an actuator couplingmember 512 extending at an angle 513 from the body 511 such that theactuator assembly 502 (or actuator assembly 302, 402, or 402 a describedherein) may couple to the actuator coupling member 512 and drive theaperture drive mechanism 510 while being disposed next to the radiationdetector housing 304 and within the vacuum chamber 218 of the imagingsystem 200. In the implementation shown in FIGS. 5A-5H, the actuatorcoupling member 512 includes a rod 514 extending down from andperpendicular to the body 511 of the aperture drive mechanism 510. Inthis implementation, the actuator assembly 502 includes an actuator arm516 having a recess 518 (e.g., defined by pins 519 and 520 as best seenin FIG. 5I) on one end 522 (i.e., the second end) of the actuator arm516. The recess 518 is adapted to engage and laterally retain the rod514 of the actuator coupling member 512 so that the actuator arm 516controls the lateral movement of the aperture drive mechanism 510. Asfurther discussed below, the actuator assembly 502 includes an actuator523 operatively coupled to another end 524 (i.e., the first end) of theactuator arm 516 and adapted to control the rotational movement of theactuator arm 516.

In an alternative implementation, instead of a recess 518, the actuatorarm 516 may have a rod 365 on the one end 522 (consistent with the rod365 on the actuator arm 916 in FIGS. 9A and 9B discussed herein), wherethe rod 365 extends toward the aperture drive mechanism 510. In thisimplementation, the actuator coupling member 512 of the aperture drivemechanism 510 may have a flange 368 having an opening 369 instead of arod 514 consistent with the aperture drive mechanism 362 in FIG. 3F orthe aperture drive mechanism 910 in FIGS. 9A and 9B. As previouslydiscussed, the flange opening 369 is adapted to receive and laterallyretain the rod 365 on the actuator arm of the actuator assembly so thatthe actuator arm controls the lateral movement of the aperture drivemechanism 510.

In the implementation of the variable aperture assembly 500 shown inFIGS. 5A-5G, the body 511 of the aperture drive mechanism 510corresponds to a drive ring adapted to rotate about the base ring 504 insliding contact with the one or more flanges 509 extending from theouter surface 508 of the base ring 504. To facilitate a sliding contactcoupling between the drive ring 511 and the base ring 504, the drivering 511 may have an inner diameter 525 that is equal to or larger thanthe outer diameter 507 of the base ring 504.

The plate 526 having the first aperture 528 is engaged or attached tothe base ring 504 such that the first aperture 528 is disposed over thewindow 206 of the housing 304. In the implementation shown in FIGS.5A-5G, the base ring 504 has an upper surface 530 and a plurality ofpivot pins 532 a-532 d extending from the upper surface 530. The plate526 also has an upper surface 534 defining a number of openings 536a-536 d each operatively configured to receive and retain acorresponding one of the pivot pins 532 a-532 d so that the firstaperture 528 is disposed over and accurately aligned with the window 206of the housing 304. Alternatively, the base ring 504 may be formed toincorporate the plate 526 so that the base ring 504 has the firstaperture 528.

Each of the aperture blades 538 a-538 d is operatively coupled to thebase ring 504 or the plate 526 so that each aperture blade 538 a-538 dis adapted to move laterally relative to the first aperture 528. In theimplementation shown in FIGS. 5A-5H, each aperture blade 538 a-538 d hasa first end 542 a-542 d, a second end 544 a-544 d, and a front edge 546a-546 d. The first end 542 a-542 d of each blade 538 a-538 d has a pivotopening 550 adapted to receive a respective one the pivot pins 532 a-532d circumferentially spaced on the upper surface 530 of the base ring504.

The drive ring 511 has a plurality of drive pins 554 a-554 dcircumferentially spaced on the drive ring 511 relative to the pivotpins 532 a-532 d on the base ring 504. The first end 542 a-542 d of eachblade 538 a-538 d has a drive opening 552 adapted to receive arespective one of the drive pins 554 a-554 d such that the second end546 a-546 d of the respective blade 538 a-538 d is adapted to pivotrelative to the respective first end 542 a-542 d when the drive ring 511is rotated about the base ring 504.

As further described herein, the front edge 546 a-546 d of each apertureblade 538 a-538 d collectively define a second aperture 548 disposedover the radiation detector housing's window 206 in response to theactuator coupling member 512 (or rod 514) being moved in a the secondlateral direction 370 b so that the drive ring 511 is rotated in thesame direction about the base ring 504 as shown in FIGS. 5B, 5F and 5G.

In an alternate implementation, each pivot opening 550 may be defined bythe base ring 504 or the plate 526 having the first aperture 528 while arespective pivot pin 532 a-532 d is disposed on a lower surface of thefirst end 542 a-542 d of a respective aperture blade 538 a-538 d. Ineither implementation, each pivot opening 550 and the pivot pin 532a-532 d engaged in the pivot opening 550 collectively define the pivotpoint for the respective aperture blade 538 a-538 d.

In the implementation shown in FIGS. 5A-5H, each aperture blade 538a-538 d has a respective top portion 559 a-559 d and a respective lowerportion 560 a-560 d that collectively form a substantially L-shapehaving an external corner 561 a-561 d. FIG. 5H depicts an enlarged viewof one of the aperture blades (e.g., 538 d) of the variable apertureassembly 500 to illustrate the top portion (e.g., 559 d) and the lowerportion (e.g., 560 d) that define or form the L-shape and correspondingexternal corner (e.g., 561 d) of the respective aperture blade (e.g.,538 d). The lower portion 560 a-560 d of each aperture blade 538 a-538 dincludes the first end 542 a-542 d and has an outer edge 562 a-562 d.The top portion 559 a-559 d of each aperture blade 538 a-538 d includesthe second end 544 a-544 d and has an external edge 563 a-563 d. Thepivot opening 550 and the drive opening 552 of each aperture blade 538a-538 d is disposed near the respective external corner 561 a-561 d.

The drive ring 511 may also have a plurality of stop pins 558 a-558 dcircumferentially spaced on the drive ring 511 such that each drive pin554 a-554 d is disposed between a respective two of the stop pins 558a-558 d. Each stop pin 558 a-558 d is adapted to engage the externaledge 563 a-563 d of the top portion 561 a-561 d of a respective one ofthe aperture blades 538 a-538 d to stop the lateral movement thereofwhen the aperture blade 538 a-538 d is moved laterally away from thefirst aperture 528 so that the first aperture 528 is exposed. Each stoppin 558 a-558 d is adapted to engage the outer edge 562 a-562 d of thelower portion 560 a-560 d of a respective second of the aperture blades538 a-538 d to stop the lateral movement thereof when the aperture blade538 a-538 d is moved laterally over the first aperture 528 so that thesecond aperture 548 (as defined by the front edge 546 a-546 d of eachaperture blade 538 a-538 d) is disposed over the window 206. Forexample, in the implementation shown in FIGS. 5A-5H, the stop pin 558 dis disposed on the drive ring 511 between the drive pin 554 d for oneaperture blade 538 d and the drive pin 554 c for a second aperture blade538 c. The stop pin 558 d is adapted to engage the external edge 563 dof the top portion 559 d of the one aperture blade 538 d to stop thelateral movement thereof when the aperture blade 538 d is movedlaterally away from the first aperture 528 to expose the first aperture528 as shown in FIGS. 5D and 5E. The same stop pin 558 d is adapted toengage the outer edge 562 c of the lower portion 560 c of the secondaperture blade 538 c to stop the lateral movement thereof when theaperture blade 538 c is moved laterally over the first aperture 528 sothat the second aperture 548 is disposed over the window 206 as shown inFIGS. 5F and 5G.

As described herein, the drive ring 511 (i.e., the body of the aperturedrive mechanism 510) is operatively coupled to the base ring 504 viasliding engagement with the flange 509 extending from the outer surface508 of the base ring 504. The drive ring 511 is also operatively coupledto each aperture blade 538 a-538 d via a respective drive pin 554 a-554d. The aperture drive mechanism 510 is adapted to drive each apertureblade 538 a-538 d about a respective pivot pin 532 a-532 d so that eachaperture blade 538 a-538 d moves laterally away from the first aperture528 in response to the actuator coupling member 512 (which extends fromthe drive ring 511) being moved in the first lateral direction (e.g.,direction reflected by arrow 370 a in FIG. 5A). In addition, the drivemechanism 510 is adapted to drive each aperture blade 538 a-538 d in areverse direction about a respective pivot pin 532 a-532 d so that eachaperture blade 538 a-538 d moves laterally over the first aperture 528to define the second aperture 548 over the window 206 in response to theactuator coupling member 512 being moved in the second lateral direction(e.g., direction reflected by arrow 370 b in FIG. 5B).

As shown in FIGS. 5A, 5B and 5C, the variable aperture assembly 500 mayalso include a cover ring 570 having an inner aperture 572 that has asize that is equal to or greater than the size of the first aperture528. The cover ring 570 is disposed over and vertically retains orcaptivates the aperture blades 538 a-538 d to the base ring 504 and/orthe drive ring 510. In one implementation, the cover ring 570 isattached to the pivot pins 532 a-532 d so that the cover ring 570 issuspended above the aperture blades 538 a-538 d so that each apertureblade 538 a-538 d is adapted to freely rotate about a respective pivotpin 532 a-532 d between a respective pair of adjacent stop pins (e.g.,pairs 558 a & 558 b; 558 b & 558 c, 558 c & 558 d, and 558 d & 558 a).

Turning again to the actuator assembly 502 shown in FIGS. 5A, 5B and 5H,the actuator assembly 502 includes a mounting bracket 564 extendingvertically relative to the radiation detector housing 304. The actuatorarm 516 is pivotally coupled to the mounting bracket (e.g., via a pin565) such that the second end 522 of the actuator arm 516 is adapted torotate in the first lateral direction 370 a and the second lateraldirection 370 b. The actuator arm 516 may be comprised of titanium,plastic, or other poor thermal conducting material that is also low infriction to improve reliability.

In the implementation shown in FIGS. 5A, 5B and 5I, the actuator 523comprises one or more electromagnetic solenoids 523 a and 523 b. Eachsolenoid 523 a and 523 b has a drive input 574 a, a return output 574 b,and a piston 576. The drive input 574 a and return output 574 b of eachsolenoid 523 a and 523 b may be operatively coupled via the interconnect254 to an external drive motor (not shown in figures) controlled by abackend processor (not shown in figures) both of which may be disposedexternal to the vacuum chamber 218 of the imaging system 200. The piston576 of each solenoid 523 a and 523 b is adapted to move along alongitudinal axis 577 a or 577 b of the respective solenoid 523 a or 523b between an extended position (as shown for solenoid 523 a in FIG. 5Aand for solenoid 523 b in FIG. 5B) and a contracted position (as shownfor solenoid 523 b in FIG. 5A and for solenoid 523 a in FIG. 5B) basedon the respective drive input 574 a. The drive input 574 a of the firstsolenoid 523 a is opposite in polarity to the drive input 574 a of thesecond solenoid 523 b (e.g., based on a respective drive signal that maybe present on each drive input 574 a as provided by the external drivemotor) such that the piston 576 of the first solenoid 523 a moves inopposition to the piston 576 of the second solenoid 523 b. For example,the piston 576 of the first solenoid 523 a has an end 578 operativelycoupled to the first end 524 of the actuator arm 516 so that the firstsolenoid's piston 576 (based on the polarity of its drive input 574 a)is adapted to drive the second end 522 of the actuator arm 516 in thefirst lateral direction 370 a when moving towards the extended positionas shown in FIG. 5A and in the second lateral direction 370 b whenmoving towards the contracted position as shown in FIG. 5B. The piston576 of the second solenoid 523 b has an end 578 operatively coupled tothe first end 524 of the actuator arm 516 so that the second solenoid'spiston 576 (based on the polarity of its drive input 574 a) is adaptedto drive the second end 522 of the actuator arm 516 in the first lateraldirection 370 a when moving towards the contracted position as shown inFIG. 5A and in the second lateral direction 370 b when moving towardsthe extended position as shown in FIG. 5B.

In one implementation, in which the piston 576 of each solenoid 523 aand 523 b includes a metal or metal alloy having a magnetic attraction,the actuator 523 may also include one or more latching magnets 579 a and579 b disposed relative to each solenoid 523 b. In this implementation,each latching magnet 579 a and 579 b is operatively configured to holdthe piston 576 of a respective one or each solenoid 523 a and 523 b inthe piston's current position (i.e., a first position for the firstsolenoid 523 a and a second position for the second solenoid 523 b) whenthe electrical bias present on the drive input 574 a or 574 b of therespective solenoid 523 a or 523 b is removed. The current position forthe respective piston 576 of each solenoid 523 a is between the extendedposition and the contracted position of the respective piston 576. In analternative implementation, the current position may be one of thecontracted position or the extended position of the respective piston576. Thus, the aperture 528 or 548 may be maintained as each piston 576is held in its current position without having an electrical bias orpower applied to each solenoid 523 a and 523 b, inhibiting potentialthermal radiation from being generated by the actuator 523 during animage capture interval of the imaging system 200 (e.g., the intervalwhen radiation is being collected by the radiation detector 206 forimage processing).

In the implementation shown in FIGS. 5A, 5B, and 5I, the actuator arm516 has a transverse member 580 disposed near the first end 524 of theactuator arm 516 and defining (relative to the actuator arm 516) a firstmoment arm 581 a having a first distal end 582 a and a second moment arm581 b having a second distal end 582 b. The end 578 of each piston 576is operatively coupled to or near the distal end 582 a or 582 b ofeither the first moment arm 581 a or the second moment arm 581 b. In oneimplementation, the distal end 582 a and 582 b of each moment arm 581 aand 581 b has a recess 584 a or 584 b as shown in FIG. 5I adapted toengage and retain the end 578 of a respective piston 578. In thisimplementation, the actuator arm 516 having the transverse member 580functions as a rocker arm actuated by the respective pistons 576 of eachsolenoid 523 a and 523 b to move the end 522 of the rocker arm 516 inthe first lateral direction 370 a or the second lateral direction 370 b,causing the actuator coupling member 512 (or 348 in FIG. 3A, 367 in FIG.3F, 412 in FIG. 4A, 712 in FIG. 7A or 962 in FIG. 9A) to move in thesame direction to laterally drive the aperture drive mechanism 510 (or344, 410, 710 or 910) of the respective variable aperture assembly 500(or 300, 400, 600, 700, 800 or 900).

FIG. 6 depicts another implementation of a variable aperture assembly600 suitable for implementing the present invention in the infraredimaging system 200 having a radiation detector housing 602. The variableaperture assembly 600 has components (including a base ring 604, a drivering 510, aperture blades 538 a-538 d, and cover plate 570) that areconsistent with and function the same as the same components in thevariable aperture assembly 500 except the plate 526 of the variableaperture assembly 500 is incorporated into the base ring 604 of thevariable aperture assembly 600 so that the base ring 604 has the firstaperture 528. The base ring 604 is affixed to or incorporated into theradiation detector housing 602 such that the housing window (e.g.,window 206 in FIG. 5C) corresponds to the first aperture 528. In oneimplementation, the base ring 604 is formed into a cover of the housing602, via etching, a molding process, or other technique. In thisimplementation, the one or more flanges 509 extending from the outersurface 508 of the base ring 504 may be replaced by a lip 606 formedabout the circumference of the base ring 604.

FIGS. 7A-7F depict a fifth embodiment of a variable aperture assembly700 suitable for implementing the present invention. The variableaperture assembly 700 has a plurality of aperture blades operativelyconfigured to be selectively adjusted via an aperture actuator assemblyconsistent with the present invention so as to vary an aperture definedby the aperture blades between a first size shown in FIG. 7A and asecond size shown in FIG. 7B. The variable aperture assembly 700 isdepicted as operatively coupled to and actuated by the aperture actuatorassembly 302 as illustrated in FIGS. 7A and 7B. However, the apertureactuator assembly 302 may alternatively be operatively coupled to andactuated by the aperture actuator assembly 402, 402 a, 502 or anotheraperture actuator assembly consistent with the present invention.

The variable aperture assembly 700 includes a base ring 704, a plate 726having a fixed aperture 728, four aperture blades 738 a-738 d and anaperture drive mechanism 710. Although the structure and operation ofthe variable aperture assembly 700 is described as having four apertureblades 738 a-738 d, the variable aperture assembly 700 may beimplemented using one blade (e.g., 738 a) or two or more aperture blades(e.g., 738 a and 738 c) without departing from the present invention.

As shown in FIGS. 7A-7F, the plate 726 is engaged or attached to thebase ring 704 such that the first aperture 728 is disposed over theinner or first opening 706 of the base ring 704 and over the window 206of the housing 304. The first opening 706 of the base ring 704 isobscured from view in FIG. 7C by the plate 726 but may be defined tocorrespond to or have a larger size than the first aperture 728 of theplate 726. The base ring 704 is mounted on the radiation detectorhousing 304 such that the first opening 706 of the base ring 704 and thefirst aperture 728 of the plate 726 are each disposed over and in axialalignment with the window 206 of the housing 304. As previouslydiscussed, the base ring 704 and the plate 726 may each be comprised ofa conductive metal or alloy that allows heat produced by the variableaperture assembly 700 or received from radiation incident on thevariable aperture assembly 700 to be dissipated via the housing 304. Theplate 726 has a circular outer edge 729 that defines a rim 707 along anouter perimeter 709 of the base ring 704.

The aperture drive mechanism 710 has a body 711 and an actuator couplingmember 712 extending at an angle 713 from the body 711 such that theactuator assembly 302, 402, 402 a, or 502 may couple to the actuatorcoupling member 712 and drive the aperture drive mechanism 710 whilebeing disposed next to the radiation detector housing 304 and within thevacuum chamber 218 of the imaging system 200. In the implementationshown in FIGS. 7A-7F, the actuator coupling member 712 includes a rod714 extending down from and perpendicular to the body 711 of theaperture drive mechanism 710. In an alternative implementation, theactuator coupling member 712 of the aperture drive mechanism 710 mayhave a flange 368 having an opening 369 instead of a rod 714 consistentwith the aperture drive mechanism 362 in FIG. 3F and the aperture drivemechanism 910 in FIGS. 9A-9C. In either implementation, the second end360, 422, or 522 of the actuator arm 354, 416, or 516 may be adapted toengage and laterally retain the rod 714 or the flange 368 of theactuator coupling member 712 so that the actuator arm 354, 416, or 516controls the lateral movement of the aperture drive mechanism 710 asdescribed herein.

In the implementation of the variable aperture assembly 700 shown inFIGS. 7A-7F, the body 711 of the aperture drive mechanism 710corresponds to a drive ring adapted to rotate about the outer edge 729of the plate 726 in sliding contact with the rim 707 of the base ring704. To facilitate a sliding contact coupling between the drive ring 711and the base ring 704, the drive ring 711 may have an inner diameter 725that is equal to or larger than the outer diameter 713 of the plate 704.

The plate 726 has an upper surface 730 and a first plurality of guidepins 732 a-732 d circumferentially spaced on the upper surface 730 ofthe plate 726. The drive ring 711 has a plurality of drive pins 754a-754 d circumferentially spaced on the drive ring relative to the guidepins 732 a-732 d on the plate 726. In the implementation depicted inFIGS. 7A-7F, the drive ring 711 has circumferentially spaced lobes 755a-755 d that extend from an outer edge 756 of the drive ring 711. Inthis implementation, each drive pin 754 a-754 d is disposed on arespective lobe 755 a-755 d of the drive ring 711.

Each of the aperture blades 738 a-738 d is operatively coupled to thebase ring 704 or the plate 726 so that each aperture blade 738 a-738 dis adapted to move laterally relative to the first aperture 728. In theimplementation shown in FIGS. 7A-7F, each aperture blade 738 a-738 d hasa first end 742 a-742 d, a second end 744 a-744 d, and a front edge 746a-746 d. Each aperture blade 738 a-738 d also has a first guide pintrack 750 a-750 d running in a direction substantially parallel to acorresponding radial axis 260 a-260 d of the window 206 of the radiationdetector housing 208 or 304 as shown, for example, in FIG. 7C. Inaddition, each aperture blade 738 a-738 d has a drive pin track 752a-752 d running in a direction substantially diagonal to the first guidepin track 750 a-750 d of the respective aperture blade 738 a-738 d. Eachof the drive pins 754 a-754 d is operatively coupled to the drive pintrack 752 a-752 d of a corresponding one of the aperture blades 738a-738 d such that each drive pin 754 a-754 d travels along the drive pintrack 752 a-752 d of the corresponding aperture blade 738 a-738 d inresponse to the drive ring 711 being rotated about the outer edge 729 ofthe plate 726.

Each of the first guide pins 732 a-732 d is operatively coupled to thefirst guide pin track 750 a-750 d of a corresponding one of the apertureblades 738 a-738 d such that each first guide pin 732 a-732 d travelsalong the first guide pin track 750 a-750 d of the correspondingaperture blade 738 a-738 d in response to the drive pin 754 a-754 dtraveling along the drive pin track 752 a-752 d of the correspondingaperture blade 738 a-738 d. Each aperture blade 738 a-738 d is adaptedto move laterally away from the first aperture 728 along the radial axis260 a, 260 b, 260 c, or 260 d of the window 206 corresponding to thefirst guide pin track 750 a, 750 b, 750 c, or 750 d of the apertureblade 738 a-738 d in response to the drive ring 711 being rotated aboutthe plate 726 and the base ring 704 in the first lateral direction 757 aas shown in FIG. 7A. In addition, each aperture blade 738 a-738 d isadapted to move laterally over the first aperture 728 along the radialaxis 260 a, 260 b, 260 c, or 260 d of the window 206 corresponding tothe first guide pin track 750 a, 750 b, 750 c, or 750 d of the apertureblade 738 a-738 d in response to the drive ring 711 being rotated aboutthe plate 726 and the base ring 704 in the second lateral direction 757b.

In one implementation, to ensure each aperture blade 738 a-738 d doesnot rotate substantially when traveling along the radial axis 260 a-260d of the window 206 corresponding to the first guide pin track 750 a-750d of the respective aperture blade 738 a-738 d, each aperture blade 738a-738 d may include a second guide pin track 758 a-758 d running in adirection substantially parallel to the first guide pin track 750 a-750d of the respective aperture blade 738 a-738 d. In this implementation,the plate 726 has a second plurality of guide pins 760 a-760 dcircumferentially spaced on the plate 726. Each of the second guide pins760 a-760 d is operatively coupled to the second guide pin track 758a-758 d of a corresponding one of the aperture blades 738 a-738 d suchthat each second guide pin 760 a-760 d travels along the second guidepin track 738 a-738 d of the corresponding aperture blade 738 a-738 d inresponse to the drive pin 754 a-754 d traveling along the drive pintrack 752 a-752 d of the corresponding aperture blade 738 a-738 d.

The front edge 746 a-746 d of each aperture blade 738 a-738 dcollectively define a second aperture 748 disposed over the radiationdetector housing's window 206 in response to the actuator couplingmember 712 being moved in a the second lateral direction 757 b so thatthe drive ring 711 is rotated in the same direction about the plate 726and base ring 704 as shown in FIG. 7B. In one implementation, the frontedge (e.g., 746 a) of each aperture blade (e.g., 738 a) overlays andaligns with the front edge (e.g., 746 b and/or 746 d) of an adjacentaperture blade (e.g., 738 b and/or 738 d) such that a portion of thefront edge 746 a-746 d of each aperture blade 738 a-738 d defines thesecond aperture 748. As illustrated in FIGS. 7D-7F, the portion of thefront edge 746 a-746 d of each aperture blade 738 a-738 d that definesthe second aperture 748 decreases as each aperture blade 738 a-738 d ismoved over the first aperture 728 along the radial axis 260 a, 260 b,260 c, or 260 d of the window 206 corresponding to the first guide pintrack 750 a, 750 b, 750 c, or 750 d of the respective aperture blade 738a-738 d.

In one implementation of the variable aperture assembly 700 asillustrated in FIGS. 7A-7F, the drive pin track 752 a-752 d of eachaperture blade 738 a-738 d defines a lateral travel range for therespective aperture blade 738 a-738 d. In this implementation, eachdrive pin track 752 a-752 d has a first terminal 780 a adapted to engageand stop the travel of a respective drive pin 754 a-754 d when theactuator coupling member 714 is moved in the first lateral direction 757a so that the respective aperture blade 752 a-752 d is driven laterallyaway from the first aperture 728 to a first position as shown in FIGS.7A and 7D. Each drive pin track 752 a-752 d also has a second terminal780 b adapted to engage and stop the travel of the respective drive pin754 a-754 d when the actuator coupling member 714 is moved in the secondlateral direction 757 b so that the respective aperture blade 752 a-752d is driven laterally towards and over the first aperture to a secondposition as shown in FIGS. 7B and 7F. In an alternative implementation,instead of the drive pin track, the first guide pin track 750 a-750 d ofeach aperture blade 738 a-738 d may have respective terminal ends thatdefine the lateral travel range for the respective aperture blade 738a-738 d.

In the implementation depicted in FIGS. 7A-7F, the drive pin track 752a-752 d of each aperture blade 738 a-738 d has a linear shape so thatthe respective blade 738 a-738 d may be incrementally driven in a linearmanner by a corresponding drive pin 754 a-754 d, enabling the secondaperture 748 to be incrementally varied in size in accordance with thetravel of each drive pin 754 a-754 d between the first and secondterminals 780 a and 780 b of the respective drive pin track 752 a-752 d.For example, FIG. 7E depicts the variable aperture assembly 700 in astate where the aperture blades 738 a-738 d have been adjusted via eachdrive pin 754 a-754 d traveling in the drive pin track 752-752 of arespective blade 738 a-738 b (where each drive pin 754 a-754 d may beactuated by the aperture actuator assembly 302, 402, 402 a, or 502 asdescribed herein) between the first and second terminals 780 a and 780 bof the respective drive pin track 752 a-752 d so that the aperture 748defined by the aperture blades 738 a-738 b has a corresponding size thatis smaller than the first size (e.g., the size of the first aperture)shown in FIG. 7A and larger than the second size shown in FIG. 7B.

In an alternative implementation, the drive pin track 752 a-752 d ofeach aperture blade 738 a-738 d may have a non-linear shape. Forexample, in the implementation depicted in FIGS. 8A and 8B, an variableaperture assembly 800 is shown that has aperture blades 838 a-838 bconsistent with the aperture blades 738 a-738 d of the variable apertureassembly 700, except each aperture blade 838 a-838 b of the variableaperture assembly 800 has an “S” shaped track 852 a-852 d that is anon-linear track for controlling the movement of the respective apertureblade 838 a-838 b and the size of the aperture 748 collectively definedby each of the front edges 746 a-746 d of the aperture blades 838 a-838b as discussed herein. In this implementation, the S-shape of each track852 a-852 d enables greater sensitivity in varying between larger sizesof the aperture 748 as each drive pin 754 a-754 d travels near the firstterminal 780 a of the respective S-shaped drive track 852 a-852 d andbetween smaller sizes of the aperture 748 as each drive pin 754 a-754 dtravels near the second terminal 780 b of the respective S-shaped drivetrack 852 a-852 d. This implementation may be desirable for a radiationdetector housing 304 that may be employed in a family of imaging systems200 in which each system requires switching between a narrow and a widefield of view optical system having range stops between, for example f/6and f/3.

As shown in FIGS. 7A, 7B and 7C, the variable aperture assembly 700 mayalso include a cover ring 770 having an inner aperture 772 that has asize that is equal to or greater than the size of the first aperture 728of the plate 726. The cover ring 770 is disposed over and verticallyretains or captivates the aperture blades 738 a-738 d to the base ring704 and/or the drive ring 711. In one implementation, the cover ring 770is attached to one or more of the guide pins 732 a-732 d so that thecover ring 770 is suspended above the aperture blades 738 a-38 d so thateach aperture blade 738 a-738 d is adapted to move relative to the guidepin tracks 750 a-750 d and 758 a-758 d of the respective aperture blade738 a-738 d.

FIGS. 9A-9C depict a seventh embodiment of a variable aperture assembly900 and a fifth embodiment of a corresponding aperture actuator assembly902 suitable for implementing the present invention in the infraredimaging system 200 having a radiation detector housing 304. Thecomponents of the aperture actuator assembly 902 correspond to andfunction the same as the aperture actuator assembly 502 as describedherein, except the actuator assembly 902 employs an actuator arm 966having a rod 365 instead of an actuator arm 516 having a recess 518 asfurther discussed below.

The variable aperture assembly 900 includes a base ring 904, a plate 926having a fixed aperture 928, a plurality of aperture blades 938 a-938 b,and an aperture drive mechanism 910. The base ring 904 has a firstopening 906 and mounted on the radiation detector housing 304 such thatthe first opening 906 is in axial alignment with the window 206 of thehousing 304. The base ring 904 may be mounted to the radiation detectorhousing 304 via epoxy, soldering, or other fastening technique. Aspreviously discussed, the base ring 904 and the plate 926 may each becomprised of a conductive metal or alloy that allows heat produced bythe variable aperture assembly or received from radiation incident onthe variable aperture assembly to be dissipated via the housing 304.

In the implementation shown in FIGS. 9A-9C, the base ring 904 has anupper surface 907 defining a plurality of stop pin openings 908 a and908 b each operatively configured to receive and retain a correspondingstop pin 909 a and 909 b. Each stop pin opening 908 a-908 b andcorresponding stop pin 909 a-909 b (when received in the respective stoppin opening) are disposed on the upper surface 907 of the base ring 904so that each stop pin 909 a-909 b is adapted to engage and stop thelateral movement (relative to the first aperture 928) of one of theaperture blades 938 a-938 b when the blade 938 a-938 b is moved awayfrom the first aperture 928 as shown in FIG. 9A and is adapted to engageand stop the lateral movement of another of the aperture blades 938a-938 b when the blade 938 a-938 b is moved towards or over the firstaperture 928 as shown in FIG. 9B.

The upper surface 907 of the base ring 904 also defines a plurality ofpivot pin openings 912 a, 912 b and 914 each operatively configured toreceive and retain a corresponding pivot pin 916 a, 916 b or 918. Asfurther described below, each pivot pin 916 a, 916 b, and 918 isoperatively configured to engage either one of the aperture blades 938a-938 b or the aperture drive mechanism 910 to allow the respectivecomponent to rotate relative to the base ring 904.

The plate 926 also has an upper surface 930 defining a number ofopenings 932 a-932 b and 934 each operatively configured to receive andretain a corresponding one of the pivot pins 916 a, 916 b and 918 sothat the first aperture 928 is disposed over and aligned with the basering 904 and the window 206. The plate 926 may be interchanged withother plates 926 that have a different sized aperture 928 to enable thefixed aperture 928 to be varied depending on the optics system (notshown in the figures) and the corresponding field of view of the imagingsystem 200. Alternatively, the base ring 904 may be formed toincorporate the plate 926 so that the base ring 904 has the first, fixedaperture 928.

Each of the aperture blades 938 a-938 b are operatively coupled to thebase ring 904 or the plate 926 at a pivot point so that each apertureblade 938 a-938 b is adapted to move laterally relative to the firstaperture 928 and the vertical axis 224 of the radiation detector housing304. In the implementation shown in FIGS. 9A-9C, each aperture blade 938a-938 b has a first end 942 a or 942 b, a second end 944 a or 944 b, anda front edge 946 a or 946 b. The first end 942 a-942 b of each blade 938a-938 b has a pivot opening 950 (e.g., the pivot point) adapted toreceive a corresponding one of the pivot pins 916 a and 916 b tooperatively couple the respective blade 938 a-938 b to the base ring 904and/or the plate 926 so that the second end 944 a or 944 b of theaperture blade 938 a or 938 b is adapted to be pivoted relative to thefirst end 942 a or 942 b enabling the aperture blade 938 a-938 b to movelaterally relative to the first aperture 928.

The first end 942 a-942 b of each of the aperture blades 938 a-938 b isalso operatively coupled to a respective one of two ends 956 a and 956 bof the aperture drive mechanism 910 so that the aperture drive mechanism910 controls the lateral movement of each blade 938 a-938 b relative tothe first aperture 928. In the implementation shown in FIGS. 9A-9C, thefirst end 942 a-942 b of each blade 938 a-938 b also has a drive opening952 and each end 956 a-956 b of the aperture drive mechanism 910 has acorresponding drive opening 953. In this implementation, the first end942 a or 942 b of each of the aperture blades 938 a and 938 b isoperatively coupled to a respective one of two ends 956 a or 956 b ofthe aperture drive mechanism 910 via a respective drive pin 954 a or 954b. Each drive pin 954 a and 954 b is inserted into and retained by thedrive opening 952 of the respective aperture blade 938 a and thecorresponding drive opening 953 at either end 956 a or 956 b of theaperture drive mechanism 910.

As further described herein, the front edge 946 a or 946 b of eachaperture blade 938 a-938 b collectively define a second aperture 948disposed over the radiation detector housing's window 206 in response tothe aperture drive mechanism 910 (and the drive pins 954 a and 954 b)being moved in a second lateral direction 957 b so that each apertureblade 938 a-938 b is moved towards or over the first aperture 928 asshown in FIG. 9B.

The aperture drive mechanism 910 has a body 960 and an actuator couplingmember 962 extending at an angle 963 from the body 960 such that theactuator assembly 902 (or actuator assembly 302, 402, 402 a, or 502described herein) may couple to the actuator coupling member 962 anddrive the aperture drive mechanism 910 while being disposed next to theradiation detector housing 304 and within the vacuum chamber 218 of theimaging system 200. In the implementation shown in FIGS. 9A-9C, theactuator coupling member 962 includes a flange 368 having an opening 369extending down from and perpendicular to the body 960 of the aperturedrive mechanism 910. In this implementation, the actuator assembly 902includes an actuator arm 966 having a rod 365 on one end 970 (i.e., thesecond end) of the actuator arm 966. The flange opening 369 is adaptedto engage and laterally retain the rod 365 of the actuator arm 966 sothat the actuator arm 966 controls the lateral movement of the aperturedrive mechanism 910.

In an alternative implementation, instead of the actuator assembly 902,the actuator assembly 502 may be employed to actuate the variableaperture assembly 900. In this implementation, the actuator couplingmember 962 of the aperture drive mechanism 960 may have a rod 514(instead of a flange 368) consistent with the aperture drive mechanism510 in FIGS. 5A and 5B. As previously discussed, the recess 518 of theactuator arm 516 is adapted to receive and laterally retain the rod 514on the aperture drive mechanism so that the actuator arm controls thelateral movement of the aperture drive mechanism 910.

In one implementation, the body 960 of the aperture drive mechanism 910defines an inner opening 972 that is larger in size than the firstaperture 928 of the plate 926 and the second aperture 948 defined by theaperture blades 938 a-938 b. The aperture drive mechanism 910 isdisposed over the aperture blades so that the inner opening 972encompasses the first aperture 928. The pivot pin 918 pivotally couplesthe body 960 of the aperture drive mechanism 910 to the base ring 904and/or the plate 926 at a pivot point (e.g., at a pivot opening 974 onthe body 960) between the ends 956 a and 956 b of the aperture drivemechanism so that the actuator coupling member 962 is adapted to bemoved in the first lateral direction 957 a as shown in FIG. 9A or thesecond lateral direction as shown in FIG. 9B. In this implementation,the ends 956 a and 956 b are arms extending laterally from the body 960and the actuator coupling member 962 is disposed between the ends 956 aand 956 b across the inner opening 972 from the pivot point 974 of theaperture drive mechanism 910.

When attached to the base ring 904 and/or the plate 926, the aperturedrive mechanism 910 may vertically retain or captivate the apertureblades 938 a-938 b to the base ring 904 and/or the plate 926 so thateach aperture blade 938 a-938 b is adapted to laterally rotate about arespective pivot pin 916 a or 916 b between stop pins 909 a and 909 b.As described herein, the aperture drive mechanism 910 is adapted todrive each aperture blade 938 a-938 b about a respective pivot pin 916 aor 916 b so that each aperture blade 938 a-938 b moves laterally awayfrom the first aperture 928 in response to the actuator coupling member962 (which extends from the aperture drive mechanism body 960) beingmoved in the first lateral direction 957 a shown in FIG. 9A. Inaddition, the drive mechanism 910 is adapted to drive each apertureblade 938 a-938 b in a reverse direction about a respective pivot pin916 a or 916 b so that each aperture blade 938 a-938 b moves laterallyover the first aperture 928 to define the second aperture 948 over thewindow 206 in response to the actuator coupling member 962 being movedin the second lateral direction 957 b as shown in FIG. 9B.

In the implementation shown in FIGS. 9A-9C, each stop pin 909 a and 909b (e.g., when received in a respective stop pin opening 908 a or 908 b)is disposed on the upper surface 907 of the base ring 904 between thepivot pins 916 a and 916 b coupling adjacent aperture blades 938 a-938 bto the base ring 904 and/or the plate 926. Each stop pin 909 a and 909 bis positioned relative to a respective pivot pin 916 a or 916 b so thateach stop pin 909 a and 909 b is adapted to engage an external edge 976a or 976 b of one of the aperture blades 938 a or 938 b to stop thelateral movement thereof when the aperture blade 938 a is movedlaterally away from the first aperture 928 and the first aperture 928 isexposed as illustrated in FIG. 9A. Each stop pin 909 a and 909 b is alsoadapted to engage the second end 944 a or 944 b of another of theaperture blades 938 b or 938 a to stop the lateral movement thereof whenthe other aperture blade 938 b or 938 a is moved laterally over thefirst aperture 928 so that the second aperture 948 is disposed over andin axial alignment with the window 206 of the radiation detector housing304 as illustrated in FIG. 9B.

While various embodiments of the present invention have been described,it will be apparent to those of skill in the art that many moreembodiments and implementations are possible that are within the scopeof this invention. Accordingly, the present invention is not to berestricted except in light of the attached claims and their equivalents.

1. An imaging system, comprising: a housing for a radiation detectorhaving a window disposed above and in axial alignment with the radiationdetector; a variable aperture assembly including: a base ring having afirst opening and mounted on the radiation detector housing such thatthe first opening is in axial alignment with the window, a plate havinga first aperture and adapted to engage the base ring such that the firstaperture is disposed over the window, at least one aperture blade eachoperatively coupled to the base ring, and an aperture drive mechanismhaving a body and an actuator coupling member extending at an angle fromthe body; and an actuator assembly having an actuator and an actuatorarm, the actuator arm disposed adjacent to the radiation detectorhousing in proximity to the actuator coupling member.
 2. The imagingsystem of claim 1, wherein the body of the aperture drive mechanism isoperatively coupled to the base ring and to each aperture blade suchthat the aperture drive mechanism drives each aperture blade laterallyaway from the first aperture in response to the actuator coupling memberbeing moved in a first lateral direction, and laterally over the firstaperture to define a second aperture disposed over the window inresponse to the actuator coupling member being moved in a second lateraldirection.
 3. The imaging system of claim 1, wherein the actuator armhas a first end operatively coupled to the actuator and a second endadapted to engage the actuator coupling member of the aperture drivemechanism so that the actuator controls the lateral movement of theactuator coupling member.
 4. The imaging system of claim 1, wherein: theat least one aperture blade includes a first blade having a first endrotatably coupled at a pivot point to one of the base ring or the plate,a second end adapted to be pivoted relative to the first end, and aninner portion disposed between the first and second ends, the innerportion defines the second aperture; and one of the base ring or theplate has an upper surface, a first stop pin disposed on the uppersurface away from the pivot point and a second stop pin disposed on theupper surface across the first aperture from the first stop pin and awayfrom the pivot point, the first stop pin is adapted to engage the secondend of the first blade to stop the lateral movement thereof when thefirst blade is moved laterally away from the first aperture so that thefirst aperture is exposed, the second stop pin is adapted to engage thesecond end of the first blade to stop the lateral movement thereof whenthe first blade is moved laterally over the first aperture so that thesecond aperture is disposed over the window.
 5. The imaging system ofclaim 2, wherein: the one of the base ring or the plate having the uppersurface includes a third stop pin; and the body of the aperture drivemechanism corresponds to a drive arm including a first end pivotallycoupled near the pivot point to the first blade and a second enddefining a track adapted to receive and limit the lateral movement ofthe third stop pin such that the second end opening defines a lateraltravel range for the aperture drive mechanism.
 6. The imaging system ofclaim 1, wherein: the base ring has an outer diameter defining an outersurface and a flange extending from the outer surface, and the body ofthe aperture drive mechanism corresponds to a drive ring adapted torotate about the base ring in sliding contact with the flange of thebase ring.
 7. The imaging system of claim 4, wherein the drive ring hasan inner diameter that is equal to or larger than the outer diameter ofthe base ring.
 8. The imaging system of claim 4, wherein the base ringhas a plurality of pivot pins circumferentially spaced on the base ring,the drive ring has a plurality of drive pins circumferentially spaced onthe drive ring relative to the pivot pins, and the at least one apertureblade corresponds to two or more aperture blades each having a first endand a second end, the first end of each blade having a pivot openingadapted to receive a respective one of the pivot pins and a driveopening adapted to receive a respective one of the drive pins such thatthe second end of the respective blade is adapted to pivot relative tothe first end when the drive ring is rotated about the base ring.
 9. Theimaging system of claim 6, wherein the drive ring has a plurality ofstop pins circumferentially spaced on the drive ring such that eachdrive pin is disposed between a respective two of the stop pins, eachstop pin is adapted to engage the second end of a respective one of theaperture blades to stop the lateral movement thereof when the apertureblade is moved laterally away from the first aperture so that the firstaperture is exposed.
 10. The imaging system of claim 7, wherein eachpivot pin is adapted to engage the second end of a respective second ofthe aperture blades to stop the lateral movement thereof when theaperture blade is moved laterally over the first aperture so that thesecond aperture is disposed over the window.
 11. The imaging system ofclaim 6, wherein: the drive ring has a plurality of stop pinscircumferentially spaced on the drive ring such that each drive pin isdisposed between a respective two of the stop pins, each aperture bladehas a top portion and a lower portion that collectively form asubstantially L-shape having an external corner, the lower portionincludes the first end and has an outer edge, the top portion includesthe second end and has an external edge, the pivot opening and the driveopening of each aperture blade are disposed near the external corner,and each stop pin is adapted to engage the external edge of the topportion of a respective one of the aperture blades to stop the lateralmovement thereof when the aperture blade is moved laterally away fromthe first aperture so that the first aperture is exposed.
 12. Theimaging system of claim 9, wherein each stop pin is adapted to engagethe outer edge of the lower portion of a respective second of theaperture blades to stop the lateral movement thereof when the apertureblade is moved laterally over the first aperture so that the secondaperture is disposed over the window.
 13. The imaging system of claim 1,wherein: the plate has a circular outer edge that defines a rim along anouter perimeter of the base ring, and the body of the aperture drivemechanism corresponds to a drive ring adapted to rotate about the outeredge of the plate in sliding contact with the rim of the base ring. 14.The imaging system of claim 11, wherein: the plate has a first pluralityof guide pins circumferentially spaced on the plate, the drive ring hasa plurality of drive pins circumferentially spaced on the drive ringrelative to the guide pins, the at least one aperture blade correspondsto two or more aperture blades, each aperture blade has a first guidepin track running in a direction substantially parallel to acorresponding radial axis of the window, and a drive pin track runningin a direction substantially diagonal to the first guide pin track ofthe aperture blade, each of the plurality of drive pins is operativelycoupled to the drive pin track of a corresponding one of the apertureblades such that each drive pin travels along the drive pin track of thecorresponding aperture blade in response to the drive ring being rotatedabout the outer edge of the plate, and each of the first plurality ofguide pins is operatively coupled to the first guide pin track of acorresponding one of the aperture blades such that each first guide pintravels along the first guide pin track of the corresponding apertureblade in response to the drive pin traveling along the drive pin trackof the corresponding aperture blade.
 15. The imaging system of claim 12,wherein the drive pin track of each aperture blade has a non-linearshape.
 16. The imaging system of claim 12, wherein each aperture bladehas a second guide pin track running in a direction substantiallyparallel to the first guide pin track of the respective aperture blade,and the plate has a second plurality of guide pins circumferentiallyspaced on the plate, each of the second guide pins is operativelycoupled to the second guide pin track of a corresponding one of theaperture blades such that each second guide pin travels along the secondguide pin track of the corresponding aperture blade in response to thedrive pin traveling along the drive pin track of the correspondingaperture blade.
 17. The imaging system of claim 12, wherein: eachaperture blade is adapted to move laterally away from the first aperturealong the radial axis of the window corresponding to the first guide pintrack of the aperture blade in response to the drive ring being rotatedabout the base ring in the first lateral direction, and is adapted tomove laterally over the first aperture along the radial axis of thewindow corresponding to the first guide pin track of the aperture bladein response to the drive ring being rotated about the base ring in thesecond lateral direction.
 18. The imaging system of claim 15, whereineach aperture blade has a front edge that overlays and aligns with thefront edge of an adjacent aperture blade such that a portion of thefront edge of each aperture blade defines the second aperture.
 19. Theimaging system of claim 16, wherein the portion of the front edge ofeach aperture blade that defines the second aperture decreases as eachaperture blade is moved over the first aperture along the radial axis ofthe window corresponding to the first guide pin track of the apertureblade.
 20. The imaging system of claim 1, wherein the actuator couplingmember includes a rod extending down from and perpendicular to the bodyof the aperture drive mechanism, and the actuator arm includes a recessadapted to engage and laterally retain the rod.
 21. The imaging systemof claim 1, wherein the actuator arm includes a rod extending from thesecond end of the actuator arm, and the actuator coupling memberincludes a flange extending down from and perpendicular to the body ofthe aperture drive mechanism, the flange having an opening adapted toreceive and laterally retain the rod.
 22. The imaging system of claim 1,wherein the actuator is a piezoelectric motor having an actuator rodoperatively coupled to the first end of the actuator arm and adapted tobe selectively moved between a first position to cause the actuator armto move in the first lateral direction and a second position to enablethe actuator arm to move in the second lateral direction.
 23. Theimaging system of claim 20, wherein the actuator assembly furthercomprises: a mounting bracket extending vertically relative to theradiation detector housing, the actuator arm being operatively coupledto the mounting bracket such that the second end of the actuator arm isadapted to move in the first lateral direction and the second lateraldirection; and an L-shaped linkage member operatively coupled betweenthe first end of the actuator arm and the actuator rod of thepiezoelectric motor, the linkage member having a first end pivotallycoupled to the first end of the actuator arm, a second end having aflange, and a corner pivotally attached to the mounting bracket, whereinthe actuator rod of the piezoelectric motor is adapted to engage theflange of the linkage member when moving from the first position to thesecond position such that the first end of the linkage member pivotsabout the corner of the linkage member and drives the second end of theactuator arm in one of the first lateral direction or the second lateraldirection.
 24. The imaging system of claim 21, wherein the actuatorassembly further comprises a bias member operatively coupled between thevertical bracket and a point near the second end of the linkage memberto bias the flange of the linkage member vertically when the actuatorrod of the piezoelectric motor is moved towards the first position suchthat the first end of the linkage member pivots about the corner of thelinkage member and drives the second end of the actuator in another ofthe first lateral direction or the second lateral direction.
 25. Theimaging system of claim 1, wherein: the actuator assembly furthercomprises a mounting bracket extending vertically relative to theradiation detector housing, the actuator arm being pivotally coupled tothe mounting bracket such that the second end of the actuator arm isadapted to rotate in the first lateral direction and the second lateraldirection; and the actuator comprises a voice coil motor having a wirecoil operatively configured to receive a drive current and a magnet, thewire coil being incorporated in the first end of the actuator arm andthe magnet being disposed relative to the wire coil so that the magnetdrives the first end of the actuator arm away from the magnet in apredetermined direction in response to the drive current flowing throughthe wire coil, the predetermined direction corresponding to one of thefirst lateral direction and the second lateral direction based on adirection of flow of the drive current through the wire coil.
 26. Theimaging system of claim 23, wherein: the first end of the actuator armhas an arcuate outer surface having a plurality of detents correspondingto a plurality of predetermined positions for the actuator arm; and theactuator assembly further comprises a spring pin having a first endattached to one of the bracket or the magnet and a second end disposedrelative to the first end of the actuator arm such that the spring pinis adapted to removably engage one of the plurality of detents to retainthe actuator arm in a corresponding one of the predetermined positionswhen the drive current is not flowing through the wire coil.
 27. Theimaging system of claim 23, wherein one of the actuator arm and themounting bracket has a metal portion, and another of the actuator armand the mounting bracket has a restraining magnet disposed relative toand having an attraction for the metal portion such that the restrainingmagnet is adapted to retain the actuator arm in position when the drivecurrent is not flowing through the wire coil.
 28. The imaging system ofclaim 23, wherein: the actuator arm has a plurality of detent magnetscorresponding to a plurality of predetermined positions for the actuatorarm, each detent magnet having a first polarity; and the actuatorassembly further comprises a restraining magnet having a secondpolarity, the restraining magnet being disposed on the mounting bracketrelative to the plurality of detent magnets such that the restrainingmagnet is attracted to a closest one of the detent magnets to retain theactuator arm in a corresponding one of the predetermined positions whenthe drive current is not flowing through the wire coil.
 29. The imagingsystem of claim 23, wherein: the actuator assembly further comprises aplurality of detent magnets corresponding to a plurality ofpredetermined positions for the actuator arm, each detent magnet havinga first polarity; and the actuator arm has a restraining magnet having asecond polarity, the plurality of detent magnets being disposed on themounting bracket relative to the restraining magnet such that therestraining magnet is attracted to a closest one of the detent magnetsto retain the actuator arm in a corresponding one of the predeterminedpositions when the drive current is not flowing through the wire coil.30. The imaging system of claim 1, wherein: the actuator assemblyfurther comprises a mounting bracket extending vertically relative tothe radiation detector housing, the actuator arm is pivotally coupled tothe mounting bracket such that the second end of the actuator arm isadapted to rotate in the first lateral direction and the second lateraldirection, and the actuator comprises an electromagnetic solenoid havinga drive input and a piston adapted to move along a longitudinal axis ofthe solenoid between an extended position and a contracted positionbased on the drive input, the piston having an end operatively coupledto the first end of the actuator arm so that the piston drives thesecond end of the actuator arm in the first lateral direction whenmoving towards the extended position and in the second lateral directionwhen moving towards the contracted position.
 31. The imaging system ofclaim 28, wherein the actuator further comprises a latching magnetdisposed relative to the solenoid such that the latching magnet holdsthe piston of the solenoid in a current position when electrical biaspresent on the drive input is removed, the current position beingbetween the extended position and the contracted position.
 32. Theimaging system of claim 28, wherein actuator arm has a moment armdisposed near the first end of the actuator arm, the moment arm has adistal end, the distal end has a recess adapted to engage and retain theend of the piston.
 33. The imaging system of claim 1, wherein: theactuator assembly further comprises a mounting bracket extendingvertically relative to the radiation detector housing, the actuator armis pivotally coupled to the mounting bracket such that the second end ofthe actuator arm is adapted to rotate in the first lateral direction andthe second lateral direction, the actuator arm has a transverse memberdisposed near the first end of the actuator arm and defining a firstmoment arm having a first distal end and a second moment arm having asecond distal end, and the actuator comprises a first electromagneticsolenoid and a second electromagnetic solenoid, each of the solenoidshaving a drive input and a piston having an end adapted to move along alongitudinal axis of the respective solenoid between an extendedposition and a contracted position based on the respective drive input,the drive input of the first solenoid being opposite in polarity to thedrive input of the second solenoid such that the piston of the firstsolenoid moves in opposition to the piston of the second solenoid, eachpiston has an end operatively coupled to the distal end of a respectiveone of the first moment arm or the second moment arm.
 34. The imagingsystem of claim 31, wherein the actuator further comprises a pluralityof latching magnets, a first of the latching magnets is disposedrelative to the first solenoid such that the first latching magnet holdsthe piston of the first solenoid in a first position when electricalbias present on the drive input of the first solenoid is removed, asecond of the latching magnets is disposed relative to the secondsolenoid such that the second latching magnet holds the piston of thesecond solenoid in a second position when electrical bias present on thedrive input of the second solenoid is removed.